For what it is worth. the other day i saw a tundra with 4" tips and it just looked wrong. they looked to big sticking out behind the wheels.
I kept 2.5 all the way, single in and dual out with 2.5 " tips and they look just right. 3" would probably be fine looking also in my opionion. But 4" that is pretty darn big. I think the tundra i saw had them sticking out a little far and a little low. maybe if you jamb them up under the bed a little more they might not look so over powering.
If you guys want to have true duals, make sure you don't go over 2.25 inches in pipe diameter, otherwise you won't have enough exhaust gas velocity in the lower rpms - in other words you'll lose low end torque big time. I have my exhaust exiting in front of the rear wheels with a custom x-pipe, two edelbrock sdt muffs and 4 inch tips. It sounds awesome and the low end is great. The 4 inch tips don't look too big at all if you arrange them properly. I chose them primarily for the sound. The bigger the tips are, the more top end growl you get. Smaller rolled edge tips quiet it down alot. I'm trying to get some pictures together and possibly a sound clip or two, but my camera is dead right now. I'll post these as soon as I can.
I haven't done exhaust since I had my 93 GMC and that was about 3 years ago. I had my single cat removed, new piping from headers back, true duals and 12" glasspacks with 4" chrome plated tips at a 45 out the sides. $130.
So if they give me an estimate of over $400 on my tundra I will freak out.
On a scale from 1-10 (10 being highest) how much will i benifit from an H or X piping config. Does the exhaust pressure vary that much from side to side that it needs to be balanced. Am I even on the right track with that thought?
I really want something about the same tone as my GMC. I'll see if I can get a video up of me driving it.