There are a couple of side by side pics comparing a WP20 to the OEM WP18 in this forum. It looks like the difference between a jackhammer and a small ball peen hammer.
So you're mounting sights on a Saiga 12. Interesting! Kind of like channeling that high volume of lead that it can deliver.
On the cooler. When you get going on it, you can get some antifreeze that miller sells for about 20 bucks a gallon, or the stuff that wal-mart sells for your RV water supply for about 4 bucks. In either case, distilled water is the coolant of choice.
Everlast 250EX with cooler and WP20 Torch
Millermatic Mig Welder
Gas welding setup
A bunch of Snap-On tools
And a Brain