Hooking up 4-wire 240 volt system. Tub is 10 feet from GFI disconnect. Do the ground and neutral wire have to be as large as the hot wires (6 guage)?

Some codes may require it, but realistically no.

Most larger spas with 230 volt everything usually have a neutral current draw of no more than 1 amp or so, negating the need for a monster neutral lead.

Ground wires on the other hand, are normally sized according to breaker requirements, not load requirements, which in effect reduces the size of the ground conductor significantly.

Call up a local electrician and see what they say about it...

Thanks for the input. I really appreciate the useful (and free) info on this site.