Tire Size

I currently have 30 X 9.5 tires. What is the largest I can go without having to get a lift or change the gear ratio. Its a 4x4 so I am not so much worried about the clearence, more the gear ration and how it will affect the spedometer and acceleration. Any suggestions on good tires?
I was thinking Duelers, BF Goodrich AT, or Firestone Destinations

just get out the tape measure!!! every year and model have different clearances!!!if your worried about losing power i'd stay with the size you have. every inch bigger you go drops your gear ratio .10 example= if you have 4.10 and 30" tires, 31" tires will drop it to 4.00, 32" tires will drop it to 3.90. i have 33's with 4.10 but its actually 3.90 and i noticed a loss of power and no better mileage on freeway with bigger tires!!!!