I have a friend who owns a Glock 20 and a companion Glock 29 in 10mm.
I own a Glock 23C (compensated model) and have fired a friends Glock 23 in .40 S&W.
10mm vs .40 LOADS
Beware of 10mm factory loads. Virtually all of them are down loaded to .40 S&W power levels. If you want the full power advantage of 10mm use the longer barreled Glock 20 and clock the ammunition yourself, don't necessarily trust what some salesmen tells you.
The compact Glock 29 in 10mm is almost the exact same size and weight as the Glock 23 in .40 S&W. Unless you are planning on getting an additional Glock 20 in which case magazines could be shared with your Glock 29, I recommend a Glock 23 vs the Glock 29.
Even the Glock 23 in .40 S&W can be somewhat unpleasant to shoot. The compensated model Glock 23C is much more comfortable to shoot. The comp system works.
Last edited by gunsandrockets; 11-18-2012 at 4:58 PM..