I tried most of them on my old '91 YJ.
By far the biggest gain was going to 4.88's. The TB spacer, electric fan, etc were a waste of time to be honest.
With 35's and 4.88's, you still tried anything at all to avoid the interstate, or any other 70mph road. It was a dog, and drank fuel seeing as you have to keep your foot buried to make it move.
best thing I did was swap a 4.3 and 700R4 into the rig. I actually enjoyed driving it then!
1998 XJ on 37's.JK Rubi axles with chromo shafts and ctm's, 4:1 transfer case, etc etc etc.The Cherylkee....
2003 Range Rover HSE, 4.4 Quad Cam.
1998 Range Rover 4.6 HSE
2000 4.7 4WD WJ with a rebuilt motor.
4.3/700r4/new frame buildup (YJ)....
Years to gain the hands on experience, and offer it freely.
Minutes to gain the knowledge from the internet, and quote it just as freely.