I have noticed that SSE is a very GPU reliant game. My GPU runs at 100% and my CPU runs at 15-35%
But my GPU is crap and my CPU is very good. So that sucks for me, And may affect my results.
Specs:
CPU: Intel 3570K @ 4.0GHz
GPU: GT610 1GB
RAM: 12GB 1666MHz
A couple of suggestions. Go into your GPU settings and disable anistropic filtering. For some reason my graphics hate it with SSE (I believe it is the water). With AF disabled I can run everything in game at max settings except for refractions(never really cared for that too much anyway even on SS08) and still get a smooth experience. Not sure of the FPS though but I guestimate 20 plus or minus. I can't see too much of a difference but it quadruples my frame rate with it off. You can also set everything to performance instead of quality and then start adding more until you find the sweet spot.
Not really familiar with your GPU but mine is an HD8670D with 762mb dedicated and the rest shared up to 6400mb total memory and I do OK.
Does your GPU even fall within the minimum requirements? GPU model numbers always confuse me and usually have to compare them online to see which ones are better, faster and so on. Just try dumbing down your GPU settings, you might be surprised.