Hmmmm
Lets hope it's not a huge issue - as I said above it's been dispatched already! Perhaps I should have asked a few more case questions back when I was building!
Is this likely to be a major issue?
I don't think it's a huge issue if you don't mind extra noise and higher temps, but those AFs are really quite loud above about 50% or so. A single AF120 is likely going to have to go at some speed to expel all the hot air. As I've got the extra MLs making up for it I don't run my AFs above 50% even when max load when gaming and keep them 30% at idle for near silence. AF are also just 3 pin DC fans, a lot less control than PWM MLs or similar even in bios hence me having to use Argus fan monitor to tune them for silence.
You've got vents at the top which air can escape from even without fans, but they also have plenty of space above the motherboard and mounts for up to 2 x 140MM fans or 3 X 120MM. I moved the included 140mm AFs to the top as extra exhausts and put 2 X ML 140s at the front instead, though those AFs are still decent at the front as intakes.
I'm genuinely surprised that the OCUK builders didn't try sell you at least an extra 140MM as even all Corsair's spec blurb for the case uses extra ML140s to demonstrate the optimum air flow. I think you would definitely benefit from even just one extra 140MM for exhaust at the far back top part of the case, especially as it'll be pretty much above that CPU cooler.
The good news is adding a fan to the top is very easy, even with a completed build. You can screw the fans in from the top of the case for exhaust, and can definitely neatly cable manage a single fan cable without taking the back side off.
You could add another 140MM like I did at the top front as well but it will be less effective as it's at the front and partially blocked by the 5.25 bay, though still expels a fair quantity of warmish air under load. Removing the HD drive cage is also a very easy upgrade as an option and massively improves air flow with or without putting an extra 120MM intake there.
Anyway, that's just my opinion for a virtually silent config at idle for work and quiet at gaming load rig. You can still get great performance with less fans, just noisier and hotter. Not saying my config is the best or optimum, just what works well for me with that case.
