For maximum performance with the basline medium settings, you may want to turn off shadow maps and post processing

Looking for an inexpensive GPU upgrade for BioShock? FiringSquad tested some mainstream graphics cards ranging from the GeForce 6600 GT up to the GeForce 8600 GTS. Here're results:

While it certainly doesn't hurt to have the latest high-end DX10 GeForce or Radeon graphics card, clearly you don't have to spend $400 or more to truly enjoy BioShock. With a just a couple of tweaks here and there, a $150-$200 card should be able to deliver very playable frame rates without compromising too much on image quality. The game's medium quality graphics setting really does a good job of balancing good image quality with high performance. However, if you simply must have the best image quality possible, you're going to have to game at lower resolutions like 1280x1024 with today's latest DX10 mainstream cards. The Radeon X1950 Pro also continues to put up a strong showing too by the way.

Based on the results we've seen up to this point, it looks like NVIDIA's DX10 driver for BioShock is giving their cards the performance advantage under the game's DX10 path, but clearly the Radeon HD 2600 XT is no slouch in this game once it is running under the DX9 codepath. As we noted earlier in this article, performance improves by a factor of up to 1.5X under DX9. This is simply an enormous performance improvement and we're hoping AMD can eventually bring the performance of their DX10 driver closer to this point in the game.

In all honesty though, BioShock 1.0's DX10 bug is probably a blessing in disguise. Why? Because the water ripples running in DX9 mode look terrible! While you can make an argument that the soft particles and especially the crisp shadows found in BioShock's DX10 path can be difficult to spot at times, you literally can't miss the difference between DX9 and DX10 water ripples. It really is a night and day difference! Now some of you may be thinking that dynamic water ripples aren't a big deal, but water is present everywhere in this game - you are roaming around in a underwater city after all. If you just shelled out the money for a DirectX 10 graphics card, you really owe it to yourself to at least check out BioShock's dynamic water ripples. Once you've seen how the game looks without them, it's pretty tough to go back.

Ed.note: I also recommend you to check out this BioShock tweaking guide.