Hi Chris,
The fans were running on high (you can barely hear them on high, so I left them cranked right up).
I reinstalled the Scythe ram sinks last night, and ran rthdribl to stress test it (still very stressful if you force 16xAA @ 1680x1080). Under full load they peak at appx 83/88/88. Definitely much less worrying!
It might be worth stickying the Furmark issue - it's getting quite popular for stress testing these days.
I did notice that the VRMs were about 10c hotter with the Scythe sinks than they were with the heatplate from the stock cooler. Is beefier cooling for them recommended for overclocking?
I'm tempted to go for something like this if necessary:
Chilled PC UK - Watercooling made easy, The UKs Largest Selection of Watercooling
Cheers!