[quote name='Ashwood1985' timestamp='1347356104' post='1799633']
Or simply that 'hey, if I play a 6 then why no practise all the time on that so when I'm on my 4 I know I've covered all options in hand positions!'
[/quote]
I play a 5 quite differently to a 4, taking advantage of those convenient extra notes without having to move my fretting hand. When moving on to the 4, I find I have to think a bit more, and move my fretting hand more. This is not necessarily a bad thing.
Regarding choosing which one to play on the gig, you need to consider tone and aesthetic. The 5 fits right in with my reggae band, but I have depped with a Bowie tribute on occasion, concentrating mainly on the Ziggy era, (sorry Bilbo) and the 70s P just sounds and looks right.