Can't offer anything on the PX4, but I have a Sigma as my bed gun.
Had a number of 'em over the years, and no complaints-finally moved on to the usual name dropping suspects, but saw no real reason to replace the bed gun.
It's inexpensive, works, and I can hit where I aim.
Only thing I can offer on the Sigma:
1. Folks complain 'bout the trigger-doesn't bother me, but I learned on DA revolvers.
2. Might want to add a
Hogue Handall?
3. Many folks will tell you mastering the Sigma trigger will make you a better shooter.
4. Make sure it's an 'E' (Enhanced) model-the E models had a number of fixes from the original.
5. It has a proprietary rail-if you plan on adding a light to it later, you might prefer something with a Picatinney rail, although it's probably better to get a separate light and learn how to use the light with the gun (I have a
Streamlight Nightfighter).
6. Not nearly as 'bad' as 'Net folks say-a lot of Sigma hate originally (and probably still does) came from fans of a certain polymer pistol that shall go unnamed!
If you like the feel of the Sigma, check out the trigger beforehand.
Check for rebates etc before you buy-S&W has Sigma offers on a regular basis, but $279 is pretty hard to beat.