I have Carli 3.5" E-Venture and full spring pack - with 37 x 12.5 x 18's (Toyo AT) and I have the 8" and it has all the adjustment I will ever need.
Note my truck hitch now sits 1" lower at the bottom of the hitch that it did stock - Stock my truck to bottom of hitch was 20", now with Carli 3.5 lift (which is really 1.5" on a Tremor in the front), the rear to the bottom of this hitch is actually at 19". So the front went up 1.5" and the back went down 1". So that would make me want the 8" and not a 10".
The goal of Carli was to have the truck "level" and by going up 1.5" in the front and down 1" in the back the truck is now basically level. OEM has about 2.5" of rake to take up squat of heavy load or trailer and keep the truck level.