people are getting the dynamic link out of memory error with other video cards than the gtx 970. its an adobe bug, one of the many many bugs in their software right now... this is what happens when features>stability is chosen.
the gtx 970 can use all 4gb, its just segmented to 3.5 and 0.5. it will only slow down its performance when accessing the other .5gb, not that it cant. in theory it would slow down any application that uses more than 3.5gb of memory on the gpu.