do a google search for ampacity. You can pull 55 amps with #8
That is only if both the terminals on the breaker and equipment are 90C rated.
#8 AWG is OK if all the requirements are met (assuming 52A load/min circ rating). The terminals need to be 90C rated and the wire must be 90C rated. For copper wire it needs to be something like THHN, THHW, THW-2, THWN-2, etc as per table 310.16 in the NEC. Also make sure none of the run is exposed on a rooftop.
Yes! As others have suggested, just google "ampacity" and you'll get the answer, be safe and don't even consider undersized electrical wiring on high load circuits...
He may be a master electrician but #6 is the absolute most conservative choice and overkill. The code allows #8 for 55A as long as the breaker terminals, equipment terminals and insulation all meet the 90C rating requirements.