If you have 2 identical slicks, 1 with a tube and 1 without, would running more air pressure in the tire without the tube give the same benefits (stiffen tire, increase sidewall life) of running a tube at a lesser air pressure? If so, how much more air pressure would it take?

No, the added rubber of the tube is what stiffens the tire.

I run tubes to help the sidewalls last as long as the "tread" area. A few years ago I got a flat between rounds late in a race and didn't have time to patch the tube. I removed the bead screws from the outside of the rim, broke the bead down and pulled the tube out with the rim still on the car. Flipped the tire bead back on the rim, put a few rim screws back in and aired the tire back up. Plugged the slick and went back to the staging lanes. Finished the race like that and the car hooked and went straight just like before, no problems. (same air pressure with or without a tube)

Brian

We spent years trying NOT running tubes in the heads up car, it is a 29.5x10.5 tire. IN the end it just flat works better with the tubes and we get a tad more life from the tire. FWIW we have been 1.08 60' with it as an NA SB. But it also has alot of do with the power being made, shocks and chassis set up. If you run a low/moderately powered car it likely would make little to no difference. When you start hitting the tire hard it defintely does. When it comes to big tires the results don't seem to be so clear, as the weight of the tube plays a roll. I have tried both in my personal big tire stuff and FWIW I dont run tubes in any of them now. But I dont make crazy power for that sized tire either, but have been 1.01 60' in a door car and dragster

I haven’t ran a tube in well over 30 years. Front or rear. Never will again

I use my hand and feel the slicks from the inside to the outside and use the air pressor to get a uniform feel on the slicks, radial or bias ply.
On the bias ply slicks if you feel the outer and inner edges and they are rough and same roughness in the middle that tire needs more air in them to get the same feel, texture all the way across.
If most of the tire is rough but the edges are smooth let some air out, I use 1/2 Lb. increments to get me in the ballpark and fine tune from their in 1/4 lb. increments, I try and use as much pressure in them that I can as long as they don't spin IHTHs

Garrett I experimented with tubes in my car and the only differences were slower ET due to added weight, with 32X14 slicks the tubes were HEAVY, and less leakage between races. Nice, but air is free...

I run tubes in M/T 10.5wx31. The 60fts are as good when the tread is gone as when they're new. About 150 passes. 1.25-1.30 60ft depending on ignition timing and ballast.
Doug

Like Al stated, different cars experience different things with tubes and I couldn't agree more. My car went faster when I put tubes in from tubeless. I wish I was joking. But the way my car was setup to work, without tubes, even with a stiff sidewall slick, it needed more sidewall support because when I put the tube in and the car launched I was shocked because it worked so much better. I just put 203 runs on a set of Hoosier 32x13.5W slicks with tubes. Plenty of rubber left on the slick, but I felt the sidewalls were starting to show weakness. I had new ones already purchased, so I put them on and hopefully get another 200 runs out of them. Without tubes, I got 130 runs before the sidewalls were gone. But again, everyone's car is different.