Considering a jump

Ok...due to my current budget and almost total lack of experience im gonna ask for some opinions. First..im considering making the jump from a 4 string to a 6, that alone has me a bit worried but im not too sure why. 2. I play in a metal band and was wondering if the six string I was considering buying (Ibanez BTB 406) could instead of taking the High C could be replaced w/ a Low F#...i dont know anything about neck tensity or anything so I'm just looking for input. So stories about jumping from 4 to six or techincal info on the bass would be helpfull...thanks

-cap