Just another point of reference on my JKU. I have a stock ported steering box, the PSC pump and reservoir, PSC high pressure line, cooler and a PSC 1.75 x 6.75 ram. I'm running 37's. I've only noticed lag one time when pulling into the driveway when my idle dropped for a second. It may be that the XD box requires more pressure than the stock box and that's where the lag is coming from. Aside from that, it's rock solid, It turns as soon as you want it. On the highway it's a bit touchy, but you get used to it, make sure your alignment is spot on and you have enough caster, I believe PSC recommends 7+ degrees. I put a 2 door box into my 4 door actually, I think the slower ratio helps with the highway driving.
In my opinion, the XD box is great, but, adding a ram is going to make a more noticeable difference. It takes a lot of stress off the box and drag link, it also acts as an incredible steering stabilizer. Seriously, it transforms your steering, you're essentially removing any slop from the TRE's on the drag link and steering directly on the tie-rod. The cost of my set-up is pretty close to buying the XD box.
All that said, if my box fails, I'll surely get the XD for peace of mind.
