Personally, I think 10 gauge is simply overkill unless you're going great distances. 12 gauge is more than adequate for home use.
It seems you're in the perfect position to solve this mystery for yourself by doing an informal test.
Simply get some reasonable cables and try them in that bi-wired situation. Heck, just get some 12 gauge from Home Depot for starters. After the prices you paid, or are prepared to pay for the others this should be essentially, if not literally, pocket change.
Since they will both be run to the same posts on the amplifier, switching them at the speaker side for testing should be a snap. If you have an interested friend to do the switching for you, you might try an informal blind test.
Please report back with your results.