The other place you can try if you happen into Calgary on a shopping trip is ProLine in Inglewood. They usually have them, and their prices tend to be reasonable (at least, last time I picked up a 452 mag from them about a year ago they were reasonable). Worth the visit just to see what a real gun shop is supposed to look like.
I have a couple metal 5 rounders, couple poly 5's, and some poly 10's... The poly are a hair wider and fill out the magwell, so no movement, but they "glide" better going in than the metal ones - no metal on metal friction, if that makes any sense.
I'm not worried about either holding up for the life of the rifle.