You are too big for a KX65. The two bikes are quite different in size. The drz is more comparable to an 85cc two stroke as far as size goes. Go for a KX85 if you have been riding a while, go for the drz125 if you are just getting in to dirt bikes...
If you are still growing, go for a big wheel model 85 or four stroke 125... such as a KX100 or DRZ125L... Dont be afraid to check out other brands too, they all make excellent models that compare to one another and performance and reliability are pretty similar among the brands when it comes to 85s and play bikes...
Top speed dosent really matter, because in motocross its about how fast it gets up to speed not how fast it tops out...