A 30" tire on a 17" wheel will look goofy - especially on an XJ. It will also be a poor combination for even moderate offroading. With a bit of trimming and bumpstopping, you could run 31's on a 1.5-2" lift. That would look and work best on 15" wheels.
You do realize the JK wheels use a different bolt pattern? You can buy spacers to convert to the XJ 5x4.5" pattern.
'00 XJ Sport, White - almost done for now...
'11 Town and Country - people mover :-(
'88 XJ Up Country, '01 XJ Sport, '08 KK Limited, '98 XJ Parts Donor, '07 XK Limited (the Stall-ander)