Im looking at getting another 500 i have the 4 but to loud and feels like a campfire with light fast bullets so for plinking and possibly carry for fishing in ak which one 3.5 performance center or integral comp 8.38
The longer barrel gives a longer sight radius and higher bullet velocity and is probably more accurate at longer distances. When your life is on the line you want all the advantages you can get on your side!! Gary
8.38 is a lot of barrel for carry, if you wanted to hunt with it OK, but just for packing - not me. OTOH the 3-1/2 doesn't really offer much compared to your 4" in terms of carrying it; if you like the sights on the PC gun for example then OK, go for it.
A S&W 500 Magnum is going to be a very cumbersome firearm to wear when you are fishing (no matter the barrel length). Something a bit smaller might be better! The only purpose I see for the 500 is for serious Bear or Buffalo hunting when a Rifle or Shotgun will only be used as back-up. Sorry, I don't really get "plinking" with a 500, but to each his own.
The 3.5" PC would be even louder and reduce bullet velocities while the 8 3/8" is way too big to be practical while fishing - unless you are ice fishing in Polar Bear Country and mostly sitting.
How much more cumbersome would a rifle with a sling be while fishing? My general rule is "If there is an area where I need to be seriously concerned about bears, that's an area I avoid."
If you keep your 4 incher, get yourself a military shoulder holster for a 1911. Cut the inside row of stitching out and your X Frame will fit like it was made for it. The chest carry holster is quite comfortable with the X frame on board.