Got my front Bilstein 5100's installed on my 21' RST Z71 5.3L yesterday. I did the front and the rears both. I did the install for the rear's myself but didn't feel comfortable with doing the fronts.
First impressions - Quite noticeable difference/improvement in ride quality over the stock Rancho's. I understand the "more planted" feel that other guys are saying now, but I was confused about what that really meant, but the 5 mile trip home I caught on. I was torn between going with the 1.5" or 2" setting. I went with the 2" setting.
Measurements from level cement to top of wheel well before were as follows for stock: Front - Driver 38", Pass 37 7/8" Rear - Driver 39 1/8", Pass 39 1/4". Once swapping the rear shocks for the Bilsteins, the front measurements didn't change, but gained a 1/4" on the rear on each side exactly. I'm thinking that may settle out with time.
Measurements after adding the front struts to the 2" groove are as follows: Front - Driver 39 5/8", Pass 39 5/8" Rear - Driver 39 1/8" Pass - 39 1/8". I also had stock size (275/60/20) Ridge Grapplers installed to replace the stock tires. I wanted to go 285/60/20, but the cost increase/difference of over $400 from stock size, I decided not to for that small difference.
So on my setup, the 2" groove yielded 1 5/8"-1 3/4" on the front, which I am happy with because I was torn between the 1 1/2" and 2" setting, so in the middle is great. From the measurements, the front is now 1/2" higher than the rear and it does appear to be higher from an eye test. I will be adding a 1" block in the rear to hopefully get it back to at least level or a slight rake to the eye test. Just my initial thoughts. I will post photos over the weekend.