Reply by sandhill

You can not fill more than 80% of the conduit by code so my advice to you is get a 125 AMP sub panel (lug) with a 100 AMP main in the master panel and run #2 / 3 wire with ground (use UF) and also a 10 foot ground bar outside near the sub panel and no, its not over kill for a shop that has a number of 220 VAC machines as well as high current draw on the 110 equipment. Its cheaper to do it this way now because the load center the wire and breaker is not that much more then what you are buying now for the upgrade. Also check your code they may require you to use metal pipe for inside a shop. 6 gauge would only handle around 45-50 amps safely on a fun of 80 feet. Your UF rated wire which can be buried under ground should never be run in conduit due to heat build up.
My .02 for what its worth