I think they're basicly the same... Looking at this Seasonic makes the AX850... Edit: Here we go, Jonny Guru says they're basically the same
Same PSU. The only difference, is that modular cable style, and packaging. I have the Corsair AX750, a fantastic PSU, the fan doesn't even spin when system is idle. I got this one over Seasonic because it was cheaper, and Corsair has a good reputation.
I'd pay the tenner, because I'm a snob. But they are virtually identical and the warranty is longer on the Corsair. So if you intend to keep your PSU for 7yrs, fill your boots
I'd go for the Seasonic, as I'm fairly sure (if it's the new update unit) it's marginally better than the equivalent AX. And you do save £10, though I guess that depends on your budget overall as to whether that's important. Given the power supply, I'd guess not. DISCLAIMER: could be wrong
Corsair is the one I'm liking. £10 less on usual price on scan and larger warranty. Just have to be patient and wait for it to cone on today's only special.