on 09-04-2012 20:55
Strangely I went from 2.3.3 (the original firmware) to 2.3.5 without much of a hitch.
The 4.0.3 went in OK as well however Kies is buggy as hell. I kept getting BSOD with it, so I cleared as much as I could out. Run Memtest 4.10 from DOS with 100% pass. So I think that's a lot to do with it.
Anyway another option is to use ODIN and the firmware download from Sammobile.com, Obviously do this at your own risk, although to be honest it's no more perilous than Kies.