I’m speccing a similar bike now, too. Planning to use it for light touring as well as long distance tris. If you put a rack on it, you’ll appreciate disc brakes.
On a mountain bike, disk. I remember my first mtb with centre pull brakes and thought they were powerfull! Although terrible in freezing conditions, how did we manage racing on those rigid steel bikes and brakes?
Cyclo cross. DISC. No more judder. Hate fork judder. Disc is a savior.
Road racing. Rim brakes. Always said if road goes disc i’m quitting road racing. I have. The crashes are bad enough without being burnt, sliced and diced also.
Zwift, who cares, ride like a lunatic and no one gets hurt or offended by your style and tactics.
TT. Whatever floats your boat. Disc or rim. No need for brakes, just like CX!
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Possibly counter intuitive, but I think that the benefit of discs isn’t that great on mountain descents (well at least the ones in Switzerland). On a big descent, the gradients aren’t massive, typically 6-10%, there are long straights, and the tarmac is in great condition, therefore you don’t brake too much, just as you approach the bends. So long as you are a competent descender, there is little risk of heat build up in the rims. Where discs do make a difference is steep, technical descents, especially on crappy roads. Discs also make a difference in the wet
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Whilst i’m no experienced rider, this is it for me. When i go out with my friends, i seem to be able to descend and brake much more confidently. Partly being on 28s and partly having the discs compared to my mates on 25s (and below) with rim brakes.
We’ve got lots of 10-20% hills around here, that are only a few hundred metres at a time. But they’re twisty, the roads are utter shite and the drivers are 
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Without going all GrahamO, I just don’t understand this. Steep, damp roads, I’m worried about losing traction entirely and locking up / sliding out, not being able to brake enough
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In the wet, the advantage of disc brakes is that you get instant braking and you don’t have to wait for the pads to clear the water off the rims. That’s a big advantage, especially over carbon rims.
What I did find when I made the switch from rims to disc was that it was much easier to lock the brakes up in the wet because your braking power is exceeding the grip of your tyre. Having said that, it doesn’t take long to adapt and learn that you don’t have to pull the brakes really hard just because it’s raining.
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What he said.
Sounds just like UK country roads 
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GrahamO lives in the UAE, so basically he was completely detached from the conditions experienced by UK riders.
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To me this is what generated the whole disc brake market on road bikes. Disc brakes were only really seen in specialist cases when aluminium rims were the norm, tandems etc. and there was no discussion (as best I can remember) about braking adequacy for normal road bikes.
Once carbon rims became common place and brake performance became an issue (terrifyingly so in the wet in some cases) a need arose which disc brakes could fill which then got blurred into aluminium rims, which never had the same issue.
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Exactly this: In the damp, on rim brakes, I tend to drag the brakes to keep the rims dry, otherwise there is that nerve wracking moment when you brake, nothing happens for a split second, then you brake too hard as the rims dry, at least with discs, they are more consistent and I find them easier to modulate.
I recently serviced the Cervelo R5 I built last year, and sold to a club member. I built it with Prime Black wheels, on a test ride I was stunned just how good the rims brakes were and how much feel the bike had with SRAM Red Calipers, certainly in the dry they performed at least as well as my disc brakes
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And maybe this is why I’ve never experienced an issue with rim brakes. I’ve never used carbon rims.
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Excellent point, and the comment I just made about the Prime Black rims also backs this up.
I don’t get too worked up about disc vs rim brakes, both work, both are part of a complete system: My favourite bike, Cervelo r5ca has rim brakes, I don’t take it out in wet or crappy conditions as its brake / wheel combination is shockingly bad in heavy rain, although in damp conditions its not too bad
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Yes
The closer you get to mountain bike conditions the more relevant discs are: UAE, not remotely close, Switzerland, mountains - yes, but also smooth roads, In the UK, many country roads could be classified as off road 
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I have had some scary experiences with older Zipp rims in the wet! It cost me time & places. In the dry not really an issue.
I’ve had one bad experience with rim brakes.
This was with the direct mount, too.
Unforecast rain last summer whilst descending the Cat and Fiddle.
Other than that, I tend to use the correct kit for the conditions.
When I bought the BMC I chose rim brakes as I couldn’t be arsed to learn about disc brakes 
That’s my reason.
I was listening to a Mitch Docker podcast with either Hugh Carthy or forum pin up boy Lachlan Morton & they said that when descending in the peleton with their disc brakes they are wary of rim brake bikes as they start to brake much sooner. I’m guessing that means that disc brakes coupled with necessary skillset are quicker.
Who is left in the peleton with rim brakes? Is it only IG?
I’ve only got a crosser with mechanical disc brakes. Hands down my worst experience was doing the Marmotte route in the pissing rain with canti brakes on my old crosser 
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Yup. Weight is an issue for them.
It doesn’t seem to stop their descending speeds?
Sure I’ve seen some UK Postal riders on discs.