If I was a total conspiracy theorist, I'd suggest that the game peformance on the PC has been purposely gimped, a lot.
One of the worst comments i've seen on the forums lately. Are you actualy sugesting that larian made the game worse on the PC ? Like, on purpose to fail at something they've been working for years?
The game runs fine on the 6 PCs i've seen from 5 diferent persons that bought the game, ranging from a Crossfire 5870 setting to a Laptop with a 4850Mobile, going from a Core i7 up to a C2Duo mobile in default.
If you say you have a problem, try to contact larian and its technical support to sort it out, coming to the forums and trying to imply a company is doing it on purpose just because they dont like your particular setup when there are literaly millions of configs possible in the PC scene and virtualy impossible to have it 100% compatible with everything is near insulting.