A few things I've found when searching about this subject:
10-bolt pumpkin is weak, prone to cracking/ tubes coming loose
10-bolt late model axles do have 30 spline shafts, early ones have 28?
12-bolt axles are 30 spline
12-bolt pumpkin is slightly stronger, and wider
12-bolt ring gear is only about 1/4" larger diameter (OK maybe 3/8"?)
Brakes are the same between the axles... Pinion is supposedly weak in the 12-bolt. The 12-bolt U-joint is smaller, and requires a conversion U-joint or yoke change.
Overall the strength is supposed to be similar, and I've heard that the later 10-bolts are better than a 12-bolt. That being said, my '89 10-bolt has worn axle bearings and/or axles, and the pinion is leaking. The axle tubes are not leaking at the housing though. At this point, I am installing a 12-bolt from an early '80's Blazer.
Hope this helps!
Clay