I have the same problem.
In MTA 1.0.5, I had around 25 frames per second on start of a race map on any DM server with ~20 other players in the range of view. Now, after installing MTA 1.1 I have only about 10 fps in same conditions.
Other example is when I am flying a helicopter and everything I can see is my vehicle and clear sky. In MTA 1.0.5, I had around 35 fps in such situation, now I have about 20.
My PC specifications:
AMD Sempron 2200+ 1,5 GHz (single core, as you can guess)
768 MB RAM
ATI Radeon 9200 Series, SM 1.1 128 MB VRAM
Can you do something about it?