| D, if you go with a 14/39 setup you will increase top end not in gear umph!
749s standard steup is 13/39 so if you go with 14 up front then this makes final drive higher so increases top speed.
Its recommend you dont go any lower than 13 at the front so the only thing is to go up at the back.
I fitted a 41 tooth Renthal on my '03 749s with standard chain and it fits fine, i can now even use 3rd gear below 30mph!!
Any more than 41 and i would recommend a new, longer, chain though as to reduce the wheel base by too much will make the bike twitchy, altho with 41 i would say the reduction makes it turn a little quicker! | 
Threaded Mode