What will fit?
 

2005 f150 XLT 2wd, and im thinking about putting a 2.5" leveling kit on it. I dont want to spend a lot of money but i'd like to put some bigger all terrains on my stock 17"s, how big can i go?

I'd go wtih a 285/70-17 (33x11.50) tire.

I've got an '07 w/ 17 inch wheels, and an extra set of 17 inch OEM wheels. Will the 285/70R17 fit without modifications, and will the new tire size throw my speedometer off?

On a 4x4, yes.