[ViolaMum]

Silicone does insulate a little bit so I've found that cookies bake a minute or so faster on parchment and a bit less evenly. Silicone can compensate for hot spots on the pan, but parchment can't. (I bake an enormous amount - it's a little insane.)

I have no idea what Costco is selling, but I prefer Silpat mats to other brands. Absolutely nothing sticks to them, but I've found the brightly colored mats (I've had 3 different brands) are of varying quality and baked goods do sometimes stick. I've had to spray them initially and occasionally after washing. Silpat is sized for commercial pans - they fit the restaurant half-sheet pans I use perfectly. There's even a 9 inch round cake pan liner available now.

When I baked for a caterer everything we baked was on Silpat mats. Nothing ever stuck. Ever. We pretty much stored the Silpats in the pans. Wipe off the crumbs or a quick rinse was all they needed.