There is a VERY big difference between a 2.0 and 2.5" coilover! on a dyno to get a 2.0 to come close to the dampening low speed and high speed of a 2.5" coilover, you need to run upward of 250psi. The low speed dampening a 2.5" shock can control is great for your guys applications.
the 2.5" ID springs are $130a pair, and the 3.0" ID springs are $175 a pair, $45 dollar differnce... is that really that much if you have 20k in your rig? There are a ton of variables on springs no matter which ID you go with, the problem your going to run into, and what i have run into is that there arent LIGHT enough springs to get the control we like to see out of the chassis. you end up HAVING to go with a triple rate to get the car to sit low enough and then you lose your preload.
if you want to be competitive in the BITD series, you will really want to do a bypass, and do a 2.5", they are maybe 50-75$ more than the 2.0, and like i said, the difference between the two is very much a big change. the amount of dampening the 2.5" can create in the bump zone blows away a 2.0.
I wont say which MFG is the best out there, but King Shocks has great KOH and regular desert race support. They do weekly testing in barstow, and are in johnson valley the entire week of KOH working on rigs. The parts you get are the same parts that you see racing the 1000.
My strongest reccomendation isnt what brand you go with, or what size you go with, or even how many shocks... its STICKING TO WHOEVER IS GUIDING YOU! you cant go with a shock company and then ask your buddies for advice, or come on here. the companies have tuners, they do r&d, they see their results everyday, so taking advantage of their knowledge will help you make leaps and bounds when going fast in the desert! listening to 8 different guys about 8 different ways to tune your springs and valving and ride heights and such will spin your head and not get you anywhere. go to one guy, and ride it out, make the changes, get the seat time and you will be the smoothest guy out there cause you know what your truck will do, when and where...