I currently have a 2015 2 Door Sport with 14/56 coils and a teraflex leveling kit. Looking into putting some jku springs on it to gain another inch or so.
Usually how much can expect in lift in every number increase so for example how much will i gain if i go to 17/58 coils? Trying to decide which ones to purchase

 

Maybe 1/4" for every number you go up..that seems to be the best guessitmate. That seemed to be about right in my case but your mileage may vary..

 

Which did you install and how much did it yield?

 

Went from 14s to 17s in front and 54s to 59s in the rear..as I said, got about 3/4" front..1.25" rear. I have a winch/bumper up front so I've also got a 3/4" front spacer. Its also worth noting that its best to measure from ground to pinch seam on a level surface both front and rear to see what you've gained. The fender openings are different and can be deceiving. I ended up with a very slight rake..maybe 1/4" higher in the rear which was good for me..keeps it pretty level with passengers in back or towing my small trailer.

 

how about the ride comfort?

 

No noticeable ride difference for me.

 

I did the same thing previously with my JK. I went up to #59 rear springs and as previously noted, I got about 3/4". Do note that you'll only get so much as the springs are the same height, the stiffer spring just sags less. It also towed MUCH better.

On that note, I just pulled those #59 rear springs out and upgraded my suspension. If you want them, i'll give them to you. Just pay shipping.