Cognito is by far (imo) the safest (for component life), most complete kit out there.
What nick is referring to will show you how the upper control arm design will increase balljoint life, as well as increase the droop of the suspension travel.
These things are a must to correct when leveling an IFS chevy...or else youll spend more than the cost difference of the kits, in parts...prematurely.
Also, if you are sled pulling (and even if you are not)...its good to know that the same company has designed a few steering upgrades to compliment that kit. Idler and pitman arm braces, new tie rod assemblies with heim joints, etc. Cognito pretty much aimed to weed out all of the weak points on the frontend...which, really arent hard to find on that design.
Also, you asked about 6" kits...most suspension systems on the market give the rear roughly 2" less lift than the advertised front lift height. Therefore with a typical 6" kit, you will lift the rear 4", thus leveling it for the look you are going for.
Shoot me a pm if you need prices on anything....or just info.
- Jesse