there are people who like to keep a world going for months, and there are people who don't mind starting a new world every week.
I'm one of the latter, if I don't like a certain thing in a world, I just end up deleting it and making a new world. by doing that I did find some very efficient ways to start out.
so in my case going to 1.6 would be a wise choice
Don't count your chickens before they're hatched.
Been there, done that. It's more a matter of hours than a matter of days, though. Once you get to the point where you can automatically turn stuff int EMC, it all snowballs pretty fast.Do neither, take a nostalgia trip and play 1.2.5 and fully utilize EE2 without using cross mod or other exploits, should keep you busy for a week or two, maybe a few depending on how much you know about 1.2.5 mods.
EE2
TC2
RP2
BC
IC2
as the core with a few other fun mods thrown in (and of course the utility mods, NEI\Rei's\Somnia (oh how I miss this mod since 1.2.5, the new version isn't quite there yet though), just have a look around and find yourself a few interesting mods that you can get the 1.2.5 versions for throw them in, stir well and go nuts.