Hey Lance.
I have been going through the same thing you have, it seems. I have a PM2, but i have been eyeing a Southard since their release. well finally, i decided to just get one and see if i like it. and guess what? i really do.
i too have never owned a flipper. and, my first impression is that i love it. pretty slick.
the handle on the southard is about a 1/4" shorter than the PM2 (guesstimate...i did not measure). but, the blade is a little bit longer, and the useable portion is longer still, since it lacks the prominent ricasso of the PM2 (see pic).
as others have mentioned, the southard is "beefy." the handle is thicker than the PM2 and so is the blade. the PM2 has a nice tapered blade to the tip. the southard does not have that. i know you use your PM2 for fish processing (love the pics), so for that, the PM2 might still be better (see pic).
however, i did cut up some chicken tonight (cooked), and i actually preferred the southard. that may just be a honeymoon phase though. so, i am going to compare them a bit more over the next days. but, i have a feeling, i will end up selling the PM2.
one thing i never liked about the PM2 is that with the ricasso and handle shape, my hand always felt too far away from the blade. i know that there is a choil, but i don'd find that is where my hand ends up. furthermore, i felt that there was just too much handle (for me). it seems like the southard fits my hand better and that there is less "excess." (see pics)
the other thing i prefer with the southard is that the blade fits into the handle better. i always felt that the blade height was a bit too much with the PM2. i imagine it's tough for spyderco, because they have to have the hole to deploy, so they obviously need steel to fit that in. but, that means that practically, the steel extends out of the handle more than is generally necessary. since the southard is a flipper, the steel does not protrude from the handle, relatively speaking. i find that i usually toss it in my pocket rather than using the clip, so this is a plus for me.
i would recommend just getting one if you have the means. the southards are still popular, so if you don't like it, i expect you wouldn't take too much of a loss if you decided it wasn't right for you.
good luck in your quest.
-todd