Kittys used the Gold motors since - hmm well Gold motors came out - Kitty was the first to use em, and has not burnt a set out, damaged a set or anything.
24v gold Motors running on 14.4v - decent speed with 8:1 reduction and 150mm diamter wheels. 2 Stage reduction is the key to why things work decently. They dont event get warm on 14.4v and with decent bearings, higher voltages welcome
Oh we have holes drilling in Kittys gold motors, not to keep em cool (but it must be helping) but to lose weight, hehe we lost about 300g from drilling holes in them.

Mod 1 seem a decent gear size to use. have a 6mm bore? for a 8mm shaft of the gold - hmmm drill it out bigger?

Mr Stu