what do phisX and CUDA really offer. i will be using photoshop cs5
While Photoshop CS5 does not support any native CUDA-accelerated functions, CUDA does accelerate specific Photoshop CS5 plugins as you can see in this THG article: http://www.tomshardware.com/reviews/adobe-cs5-cuda-64-bit,2770-8.html
If you use certain plugins for Photoshop a lot you may want to pick a Nvidia card.
Physx is a proprietary physics engine used in some games. Since Nvidia revamped their website its hard to find the complete list of games supported, but you can see some of the modern ones at geforce.com. Click on the Physx tab on the right side to see the current games & demos that use it: http://www.geforce.com/#/GamesandApps
Some listed here too:http://en.wikipedia.org/wiki/PhysX#Title_support
FFXIV, Just Cause 2, & Crysis do not use Physx. Some popular games that use Physx are Metro 2033, UT3, Mafia II, Batman Arkham Asylum, & Mirror's Edge. If the game does not use Physx, it is an unused feature.
There are several physics engines used in games that run solely on the CPU rather than on the GPU that many developers use such as Havok & Bullet. The advantage to Physx is that it uses the parallel processing capability of a GPU to perform many calculations simultaneously, although now multi-core CPUs are more able to do the same thing.