Bioshock a cpu limited game news to me. If it is then it's not nearly as limited as total war. First hand experience with total war and that driver even on a single card was a massive improvement.
As for the omega driver I could link all the press release slides if you like that's more flash but her is a quote from AMDs own release notes.
http://support.amd.com/en-us/kb-articles/Pages/AMDCatalystOmegaWINReleaseNotes.aspx
Year over Year Performance Optimizations versus AMD Catalyst™ 13.12 WHQL*
Up to 19% more performance since launch in some games on AMD Radeon R Series GPUs
Up to 29% more performance since launch in some games on various AMD APUs.
Going back to my original point both company's make overblown claims about there drivers, even if some people think AMD do no wrong and prase the ground they work on.
And before someone starts, yes I have nVidia cards now but I've had plenty of AMD/ati CPUs and GPUs in the past. I really hope the 390x is good the GPU space badly needs to be shaken up.