I hated 3.07s with 30" tires. wasn't as fun to drive anymore (and the truck was only 10years old at the time). same truck/engine a couple years later (with a 4wd conversion) and I had 4.10s with 33s and dreamt of the day I could get 4.56 or 4.88. your mileage may vary. (but having said that, your mpgs will suck and you'll have a good chance of burning out the clutch prematurely)
something I was told by an old-timer many moons ago: half-assing something won't make it turn out half-good, it'll just be all bad. my suggestion is save your monies, be patient, and do it right all at once.
I mean, it's not like the truck will look bad on 31s. it's an MJ after all. it'll still get all the looks.