I've noticed this too using hex without numbers, On larger maps (30x30 or larger) I've started using grid instead. It doesn't seem to effect my performance or if it does its not noticeable much. But for my players with older machines they complained about it. Changing it to grid made them jump back up to smooth fluid token movement and map scrolling. It seems related to hex size, vs image size. I had it at 0.4 hex size and it was nearly impossible for those guys to do anything. 1.0 was 'bearable', while almost any size grid was fine for them. H vs V hexes didnt seem to make any difference.