CUDA is backward compatible and the features both AE and Premiere use only require v4. The software fallback might simply be there to prevent resource conflicts with Dynamic Link but generally should be nothing to worry about. Can't say anything about your otehr issue, that's not my turf things being that I know zero about Premiere CS6's little quirks...
The "headless" version of After Effects called by Dynamic Link can't use the CUDA acceleration; processing is done on the CPU.
The XDCAM EX tearing fix in Premiere Pro CS6 (6.0.2) did not get into the updates for After Effects yet.
Thanks, do you have an ETA on the tearing fix as I only use XDCAM EX footage
No, there is no ETA on the fix getting into After Effects.