Can anyone here who has both tell me what the real differences are?

Aside from the $100-$200 price difference and the odd barrel on the pc.

Hammers and triggers are different I believe. Grips obviously....all I got.

Anyone ?

If we are discussing the current production 625JM vs 625PC

PC has the partial under lug the JM had a full under lug both are currently 4-inch guns.
I prefer the full under lug for recoil management but I use my 625 for competition (5-inch full underlug).  If your going to carry more than you shoot the lighter PC might be desired

The JM uses an ECM (electrochemical machining) rifled barrel the PC has a broach-cut rifling.
In all honesty I don't think you will see a performance difference, but some still want old school.

The JM will come with a wide grooved trigger and the PC come with a narrower smooth trigger
This is totally personal preference I like the narrow smooth trigger but that is just me.

The hammers are different also the PC has a tear drop shaped thumb spur and the JM has a more squared off spur.  I also believe the PC is a forge hammer and the JM is a MIM hammer but I am not 100% sure on that.  They both use frame mounted firing pins as do all S&W revolvers now.Personally I prefer the MIM parts but there is a false perception out there that forge parts are somehow better.  I could rant on that for a page or two.

I believe the PC is a shinier finish and the JM will be bead blasted.
Personally I like the bead blasted finish as it looks better with wear on it than the shinier finish but the again is JMHO.

The grips are basically the same except for the visuals.  Its a smooth hardwood grip, round butt with no finger grooves.
That was the first thing I took off my 625.  Hate that grip, hurt the base knuckle of my thumb.  Rubber grips are what you want if your going to shoot it a lot.

The PC is supposed to have a chamfered charge holes in the cylinder to aid reloading.
It does help, especially reloading fast on the move in competition, but this is something you can do yourself with a Dremel, a Cratex-wheel and a little patience if your handy or a chamfering tool from Brownells if you like to spend money.

I believe the sights on both the PC and JM are basically the same.  I think they now both use the slip in/out front sight, which is nice.
Change out the gold bid for some fiber optics!

Rambling...

The chamfered charge holes make a HUGE difference, IMO.

The PC hammers and triggers are flash chromed, but still MIM.

I stand corrected, thanks!

I'm probably going to pick up a JM and have a bit of work done . Then it will probably be a competition/ carry gun .