Taking a snapshot with V6 takes about 5 seconds. Assuming that the messages displayed by the profiler while it takes and analyzes the snapshot have roughly the same meaning between V6 and V7, nearly all the extra time taken by V7 is in that "Filling Cache" step.
I should also note that the app being profiled continues running during that filling cache step, and some (but not all) of the ANTS UI remains responsive. For example, I can zoom the counters strip in and out, but I cannot scroll it left / right. I can also take another snapshot while the Filling Cache step runs.
As far as slowdown to the app being profiled, neither V6 nor V7 causes a noticeable slowdown. However, the problem I'm debugging now doesn't involve any of the CPU intensive parts of the app, so a for a slowdown to be noticeable, it would have to be severe enough to impact basic UI responsiveness.