;ike monster size and mad flex.
You don't necessarily need more lift to get more flex, especially with larger tires, as you will be reducing up travel to avoid clearance issues, so you can build for droop not compression.
I need two more inches (max) of suspension increase but I do not want to change trackbar mounts.
I think you'll find that with 6" of lift or more you'll want a high steer drag link, which will mean relocating the front track bar at the axle anyway. Also with more lift, things like the roll center become more important, so you may want to raise the track bar mounts at the axle end anyway to improve the roll center. Adjustable track bars would be a good idea anyway.
I will either add 2 inch spacers to my 4 inch lift coils or but 5.5 inch coils.
I want everything built the right way with no short cuts.
Answered your own question
Get the coils.
Other considerations with 6"+ of lift are things like the pinion angle. Back when I was at 5-3/4" at the front, it was difficult to get a good compromise between pinion angle and caster with an aftermarket drive shaft, which you will need. You can get away with less caster with larger tires though, so you may just be able to get it okay.
Hydro assist will help considerably in turning large tires, both on and off road, and acts as a 1500 psi steering stabilizer on the street. Not essential, but helpful.
I think the need for long arms becomes greater once you get over 6" of lift. At 6" you are most probably okay, but anything over and I'd certainly consider them.
You'll need to pay attention to rim size to run large tires, with 40's 4" of BS is too much, but you can't go much less though. They rub on plenty at the front and rear. More lift will certainly help for the street, but off-road you are going to run into some clearance issues. A sawzall will take care of most, but not the frame rubbing you'll get at the front. Setting up your bump stops correctly will help too.
As already mentioned, moving the lower shock mounts outboard slightly will help with shock clearance issues.