Here's the reason why I have a big ol' honkin spare tire carrier on my Jeep.
Bent rear tailgate from a 285/75/R16 tire mounted to the factory tire mount:
This is also the reason why you never see any pics of my Jeep with the hard top on. Since bending the rear gate my rear window on the hard top doesn't close correctly.
Personally I would put as little weight as possible on the rear gate. If you're moving up to a bigger spare I'd seriously consider getting some kind of rear tire carrier or mount it in the cargo area. However, you have have much better luck than me.