For over 600 miles, a GSXR will be extremely cramped in the legs and stressful on the wrists. Sure, you can remedy both with aftermarket parts, but only to a degree.
Consider finding a late-model Bandit for $4000 and upgrading suspension, adding hard bags and modifying comfort to taste. For about $7000 you can have a 115 hp, 80 lbs-ft bike with a bulletproof motor and decent handling at about 540 lbs wet. I did 4400 miles in 8 days in June, with the first day covering 1029. See
my page for more (though I haven't posted the ride report from this year yet).
I like the ST that Inspron mentioned, but I'm sure it's more costly.
Welcome to M-J.