I have, new glasstop,oven range, and see that #6 is common, but have new #4 wire, can I go from breaker box to hard-wire at rear of range w/ the #4?

Sure, you may want to use #6 or required size for the load, and the breaker limited by your likely smaller pigtail/whip(#6?)
Overkill never hurts, it just becomes more difficult to work with.

#4 is fine IF it fits the contacts on both the breaker and the box you will plug the range into.
I usually always got one step larger when putting in higher current wiring (Over 20 amps).