This week Croteam released big update for Serious Sam 3: BFE (the game will be released on Linux soon) - Windows users can use OpenGL renderer now. Very quick comparison (winxp, Catalyst 12.9 beta, fps counter in the right corner):
Direct3D

Code:
00:12:47 INF: Gfx API: Direct3D
00:12:47 INF: Resolution: 1920 x 1080
00:12:47 INF: Vendor: ATI (0x1002)
00:12:47 INF: Driver: ati2dvag.dll (0x6758)
00:12:47 INF: Renderer: AMD Radeon HD 6670
00:12:47 INF: Version: 6.14.10.7279
00:12:47 INF: Video memory size: 1024 MB
00:12:47 INF: Available for textures: 1116 MB
00:12:47 INF: Active GPU(s): 1
00:12:47 LOG: Processing file Content/SeriousSam3/Config/CheckDriver.lua
00:12:47 INF: Driver version: 7279 (required: 7213)
00:12:47 LOG: Loaded "D:\Steam\steamapps\common\Serious Sam 3\Bin\SfxXAD.dll".
00:12:47 LOG: Loaded "X3DAudio1_7.dll".
Code:
00:12:51 INF: AutoDetect: storing new settings: gfx_iPixelProgramVersion=40,gfx_ctConcurrentGPUs=1,sys_iGPUVendorID=4098,sys_iCPUFamily=15,sys_iCPUMHz=2793,sys_iGPUDeviceID=26456,sys_strCPUVendor=AuthenticAMD,gfx_ulVideoMemoryMB=1024,
OpenGL

Code:
00:19:47 INF: Gfx API: OpenGL
00:19:47 INF: Resolution: 1920 x 1080
00:19:47 INF: Vendor: ATI (0x1002)
00:19:47 INF: Driver: ATI Technologies Inc. (0x6758)
00:19:47 INF: Renderer: AMD Radeon HD 6670
00:19:47 INF: Version: 4.2.11903 Compatibility Profile Context
00:19:47 INF: Video memory size: 1024 MB
00:19:47 INF: Available for textures: 116 MB
00:19:47 INF: Active GPU(s): 1
00:19:47 LOG: Processing file Content/SeriousSam3/Config/CheckDriver.lua
00:19:47 INF: Driver version: 11903 (required: 12000)
00:19:47 WRN: Display driver is too old, please update it ASAP!
00:19:47 LOG: Loaded "D:\Steam\steamapps\common\Serious Sam 3\Bin\SfxXAD.dll".
00:19:47 LOG: Loaded "X3DAudio1_7.dll".
Code:
00:19:50 INF: AutoDetect: storing new settings: gfx_iPixelProgramVersion=30,gfx_ctConcurrentGPUs=1,sys_iGPUVendorID=4098,sys_iCPUFamily=15,sys_iCPUMHz=2793,sys_iGPUDeviceID=26456,sys_strCPUVendor=AuthenticAMD,gfx_ulVideoMemoryMB=1024,