I have a set of 5 Baja MTZ's (33x12.50 R17) on my 05 Wrangler. I put them on at 11,500 miles and currently have 80,500 miles on the Jeep. Yes the speedo was re-calibrated immediately following the installation. I rotate them, all 5, every oil change. I still have about 40% of the tread left on them. I keep them inflated to 28 psi. That is 69K miles, most of which is highway. We go off-road 2-3 times a year.
The MTZ's are a mud tire, but not as aggressive as some. It is quieter than most. The noise they do make is more noticeable with the hard-top on. With the soft-top, there is enough wind noise, you don't notice them at all.
Spending the money on a full size spare, and rotating it in with the other 4 is worth it IMO. You'll get 20% MORE mileage out of the set of tires. The guys at Cabot Tire & Off Road can't believe I still have the same set.
I want a new set of tires only because I'm tired of looking at these. I have had no problems out of them yet.
Hope this is helpful.