maybe your movement on stage might play a big part wen selecting bass.
i guess if you play statically(just stand there not moving around) and you nid the lows and highs, probly a 6 is a wonderful add on to ur rig. no sweat
but if u play rock punk and all dat where u move ard a lot, a 4 is safe. cuz you wont worry so much wen u lost ur fingering with all the sweat and panting and intoxication and girls in the crowd, hehe...
personally i had a yamaha 5 stringer and tho a tad heavy i managed to wear it onstage well. the fretboard mite be abit wide but i managed, phew.
now i have a 4, havent tried it onstage yet. but i guess i'll do fine( pray 4 me). its so much liter and fretboard is slim. woohoo!!!
hope my finger stretching fr playing 5 will help on my 4, hehe..
theres a lot of considerations in choosing a bass ( like comfort, tone, pups, etc) but im sharing just one outof thousands of factors which mite be helpful 2 u.
cheers!!!