I don't have full hydro, and don't know a great deal about it, but am learning because I want to change over to it on my Samurai. From what I have read, you need to size the steering valve correctly to the ram in order to get the turns lock to lock that you want. Another solid point is to determine if you want load reactive or non-load reactive.
Here is a good debate thread on load reactive vs non-load reactive. One dude dislocated his shoulder with a load reactive unit. Apparently PSC only sells load reactive steering valves.
http://pirate4x4.com/forum/showthread.php?t=703469&highlight=load+reactive