From the overclockers' forum, to which you linked:
It's not so much about overloading the CPU, it's that the PPU can create faster calculations of physics than a CPU. The CPU uses a standard logic for calculations whereas the PPU uses a specialised logic which will calculate more faster the physics effect.
The additional benifit of a PPU is that the core output will purely be dedicated to the physics whereas CPU's are load-balancing between other things. (such as active programs/OS/and everything else)
Although im no fanboy of PPU, it has it's benifits. But to be honest the downside of PPU is that it runs on a PCI slot, which means that there is a three way communication happening(cpu/gpu/ppu) at a fair rate(nothing great - although I wonder how well PhysX works on a PCI-X slot? ). Whereas, a HavocFX solution, which would be running on a graphics card will just have a two way comms between the CPU and graphics card. The obvious effect of having PhysX in the system has been the poor fps experienced by everyone (which has been demonstrated by everyone who posted here with PhysX in their system). Having said that, I can't vouch that the fps will not be reduced when HavocFX gets implemented with the graphics card...maybe it will be the same like the PPU because of the increased amount of calculations it is doing. Only time will tell im afraid
Let's hope we can see some more results from testing with PPU to see the full scale benefits of having one.
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Gigabyte 8N SLi Quad Royal nForce4 / 3.4 GHz Dual Core (950)/ LG775 Fatal1ty fan(Zalman FS-C77)/4GB DDR2/ XFX 7800GTX/ Thermaltake 560w PSU/ Thermaltake Romeo Xaser III Casing/3 x 120GB SATA/1x 80GB IDE/SAMSUNG DVDRW
^ Jealous of his setup!
Part of the issue is (so I have read) that the PPU automatically uses the highest quality graphics settings, which can cause the slow-down, too.
Still, to answer Fulcrum's question: Rome:Total War is a CPU-limited game (rather than GPU-limited), although it doesn't support the PhysX card, and won't (to my knowledge): but then again Medieval Total War 2 might ...