[John Smith]"I tried rendering a video in Vegas using "CUDA" but it doesn't seem to be all that fast?"
Sounds like a setting on the MainConcept AVC CODEC. That one does have very fast rendering for CUDA or OpenCL GPUs. Unfortunately, they stupidly have it locked to only specific GPUs, and only those that were out in 2011 or so... Main Concept was bought by DivX, who were in turn bought by Rovio, and pretty much no new work was done on the CODEC since. The whole point of CUDA and even moreso OpenCL was to do math in parallel independent of the processor (you can actually run OpenCL on x86 natively or Intel's Phi board, not just on GPUs).
Fortunately, Vegas itself doesn't have this problem, it's just in the MainConcept AVC plug-in. Make sure your nVidia drivers run OpenCL, then go to Vegas preferences, under Video options, and you should find the place to select GPU acceleration. You have to reset it to take effect. Note that Vegas, like many if not most OpenCL programs only supports on GPU at a time. This acceleration affects Vegas compositing, plugins, etc. So the more work you do, the more it helps... and it helps on editing, preview, and rendering, just not the specific CODEC.
There are some reports of sketchy OpenCL performance on nVidia boards, particular Kepler boards... they are fast on some things, weirdly sl I w on others. Though I'd certainly expect a Titan to be pretty fast at anything it does.