Yes, in general the more CUDA cores the faster the card, but that is a fairly narrow view. To get a feel for a graphics card look at benchmarks for the games/programs you want to run.
CUDA is a GPGPU programming language for Nvidia cards. Each CUDA core can run a single process. If you can imagine something like a Titan with 2880 cores compared to a quad core x86 CPU, then you see why they are useful for things other then games.