the differences between 3x, 4x, 5x HTT is fairly small, more so when you overclock, generally you don't want the HTT to be over 2000, your highly unlikely to even come close to using that, the bus controls how much data can be sent around the computer, nothing comes close to needing 8GB's of bandwith
test it out for yourself, benchmark with something at 3x, 4x and 5x