I would expect that if they've got the same humbuckers, they'll sound very similar. The added single coil and different switching will obviously give you different tones in the "in between" positions, but you can always modify the wiring to get the exact combinations you want. The exteneded scale length of the 1077XL will give you a tighter bottom end.
I've seen the 1077XL at Steve's in Toronto for about C$1500, but the last time i was in there, they were trying to blow out their overstock of 7-strings. I know Rich had prices that were comparable after shipping and taxes, but he included the UV case and his outstanding setup.
They're gorgeous guitars... i'd take a 1077XL over a 7620 any day if i were really into the RG body style. The metallic blue with full binding and those offset
abalone dots is super-classy.