I have a 2003 2500HD 2wd keep that in mind.
But anyway what I did is the 2.5" level kit from ReadyLift first before even thinking about my 6" lift. This worked great got it nice and level. Then using the keys and shock extenders from the level kit I installed my Zone Offroad 6" lift with my buddy. Easy kit to install (once again on 2wd) all bolt on part sand no extension of brake lines only minor drilling. I sit a tad nose high which is normal when doing a level and lift combo. Some people may argue but in my understanding I lifted the front a total of somewhere between 8"-8.5". The kit came with 4" blocks in the rear.
So anyway I have lifted my rear a total of 4" but with the stock blocks there it is 6" (this is where they get the 6 from on the lift kit) and have lifted my front a total of 6". Now take into account my level kit which puts me at around 8". After it was all installed I sat way nose high so we cranked those adjuster bolts down to get it level with the rear. Now I'm sitting at 6" all the way around. Then came the 37" tires. We had to crank on those adjuster bolts again to fit those puppy's under there. I can't quite remember how much we cranked on them but I know we have the same amount of threads showing on each side so it is level from side to side. We cranked on them bringing the nose up just a hair higher than the rear so we could fit the tires and of course the rear was just fine. So now I have 37" tires and am sitting slightly nose high which doesn't bother me at all you can hardly tell.
Anyway on to your topic. 8-9 inches of lift is pretty ridiculous (not saying I don't like it just saying it is really high) and would be a pretty time worthy and costly task to take on yourself. There would be extending of brake lines, more than likely cutting or grinding on frame, etc. Resulting in expert level mechanic skills. (Basically you better have prior experience and know-how on these type of things for this to be done correctly).
Now lets take a look at the 6" plus the 2"-3" torsion key lift. 6" lifts lift your vehicle to give it a total of 6"s of lift lifting the front roughly 6" and the rear roughly 4" making it even and level on both front and rear. Now remember the 2"-3" torsion lift will only raise your front end not the rear. Resulting in a higher front end. This is fine as long as you are ok with being slighlty nose high. This setup, because it is not a true 8"-9" lift, will not require the extension of brake lines and can be anywhere from moderate to expert level (depending on the truck type) mechanic skills to put on yourself.
The 6" lift no matter what would be ideal for you I think. It is a great looking lift and you can fit some pretty big tires under those fenders. Plus you always have that option to stick that 2"-3" torsion key lift in there if you wanted to fit that bigger tire. As for doing this lift yourself I would say go for it! A lot of people told me to take mine to a shop and have it done and didn't think I was capable of putting something like this on. Well I did with the help of my friend, may have taken a couple of days, but hey it was an awesome learning experience and we did it right by following the instructions exactly. There is one thing you WILL need if you plan on doing this yourself and that is a torsion bar unloading tool. Please do not do this without this tool. Very dangerous without it. You are dealing with some serious equipment here, very heavy, and under stress parts under that vehicle something you do not want to play around with so please have the correct tools. This IS one of them.
If you take it to a shop on the other hand there is no doubt it will be installed correctly and with the right tools in a matter of probably a day. This is not a bad option at all either. With this you have the safety and security of knowing it is done right and you get your truck back quickly for that busy schedule along with in some cases the shop will provide you with a warranty on their work so if anything does go wrong just take it back to them and have them fix it.
Overall I would say go with the 6" now and see how you like it, then decide on the 2"-3" keys. I promise you won't be throwing away your money on the 6" you will fall in love with the way it looks can't say the same for the keys though unfortunately, but then again it is all personal preference. Just do the 6" for now though to secure the fact that you won't be wasting time nor money.
(PLEASE REMEMBER: I am talking in terms of a 2wd truck, more specifically a 2500HD, I do not know nor have previous experience with 4wd trucks. Please do not mark my claims as false on trucks other than 2wd.)
I hope this helps you in your decision and provides some insight.
