I too prefer the FD Polar blades for compound cutting thicker woods. For aspen I would think a #5 should be plenty.
One thing I have started doing and you might want to try - whenever I am doing compound cuts, if there is a flat cut across the piece (like the bottom of a chess piece) I don't cut that on the first cut. Just treat the first cut like an inside cut and drill an entry hole to start. Maybe starting just below the bottom of the piece on one side, and finish the cut just past the bottom on the other side - don't make the bottom cut. This means the first cut is not completely cut out of the blank and has no chance of moving around while doing the second side cut. Again, drill an entry hole for the second side cut and do it the same way. Then, go back the the outside of the blank and just cut across the bottom, releasing the piece from the blank. Even when wrapping in tape and other methods, towards the end of the second cut, there is always a little room for the piece to move around if the first cut was completed and making the second cut a little inconsistent. Hope this makes sense, it is hard to explain, but it has helped me in my compound cutting is the past.
Steve