First you need to search around the forums. There's been a ton of coverage on just about every long arm set up available.
Second, you need to decide what exactly you wish to gain by going up another inch and a half and going to long arms. Once that's figured out, compare your results and see which method would work best for you.
Radius arms may or may not unload and if they do it may or may not have an impact on performance. They also bind, but it may or may not affect flex. Also, only having two attachment points to the body, they might fail catastrophically, but I've never heard of it, so it may just be fear-mongering. However, they package the easiest under the XJ and have the best clearance usually.
A 4 link is by and large the strongest, but takes up the most space and also binds. Again, it may or may not affect flex.
A 3 link has the least amount of bind, but it may not matter as many believe that the bind in the other setups doesn't occur until you've flexed past a usable point anyways. A 3 link attaches to the body in 3 places, but is missing an upper control arm so if that one fails, it could cause big problems. Again, I've never heard of that being a serious issue.
As was said, search, search, and search some more.
is a wonderful resource, full of info.
