Not even close. It appears that a modern Intel CPU can handle the entire PhysX of BL2 with a Radeon HD7970 dedicated to graphics. You get the same performance as having a GTX680 doing graphics + PhysX.
^ If that is not an accurate review, let's use a secondary source. They used a dedicated GTX690 for PhysX in BL2.
Good to know those morons at Tech Spot did a shoddy review and now that information is being posted as fact.
YOU CAN NOT RUN ALL PHYSX EFFECTS ON CPU. AS A HYBRID USER I KNOW.
TecH Spot didn't properly test PhysX, by their own admission in the comments, the author of the article only shot walls and cloths. Once you get to the fluid portion of PhysX YOUR SYSTEM WILL TANK.
Need proof?
PhysX Blood effect tanking Intel i5 2500k @ 4.4ghz w/ Radeon 7970 @ 1125/1525:
Same scene, blood clears, FPS rebounds:
Here is me testing with PhysX Mod working, notice the FPS is still crippled (this is with 9800GTX+ offloading):
Do not go by that Tech Spot article, it is poorly done and doesn't properly test PhysX in a Hybrid system.
EDIT: Updated picture with GTX 460 offloading, exact same area as the picture directly above [if you look, I'm standing on the metallic object looking at where the barrel is as I detonate it to get goo every where]
You can not run PhysX high with just a Radeon, it will tank FPS the moment you get any liquid on screen.