Different bikes, different muscles?

i am only worried because i occasionally go on long rides some times 100+ and i want to be able to just go and do them with out worrying about my legs dieing, maybe if stick to higher gears and change the position around a bit it will compensate and feel more like fixed. or maybe i should just ride the fixed all the time :s

option 2 sounds good?

why not keep it up on both bikes, reckon the aches will ease up your body will get used to it... And think of that phenomenal power you'll have when you go back to your geared steed?