I'm a big 320 fan.
FYI: If you want to go to 17 rds with your Compact, you can either spend $40 and get a Carry 'grip module' for it, or buy 17rd mags and get the X-Grip Compact magazine sleeves for them.
Here's a photo spread I put together recently for a P320 info page:
Compact on left. Compact with 17rd mag & Xgrip sleeve in the middle. On the right, a Carry. Compact and Carry use the same exact slide.
Edit: And if you want to go to 21rds. You can do it with a Compact, put the Xgrip sleeve down over the 21rd Extended Mag. Doesn't look as clean as the 21rd does in the Carry or the Full, but it's functional. No wobble.
LTC / SSC Instructor. NRA - Instructor, CRSO, Life Member.
Sig pistol/rifle & Glock armorer | FFL 07/02 SOT