Glenn,
Your correct that one should try to utilize the vendors that advertise here, and the platform is very important, because of the way some rails react to recoil, Bob Dodd's had a smaller footprint and I can remember a number of people that had complaints that the base was moving when the rail was recoiling as it hit its stop.
I think that Jay Young builds one hell of a platform but you need to consider the wait for one of his rails! I had a Jay Young rail I bought used and had to sell it when the economy turned south, but it was top notch all the way. Greg Kinsler started out with his own concept based on shooting at his home range in Tacoma which is up hill, so he added a spring system that automatically returned the rail to battery, but had some peculiar reactions. he also was milling a v grove into the bottom of the upper rail which if it was ever damaged you couldn,t repair it. Greg resolved those issues and was making one that looks and functions the same as a Jay Young rail. Bob Woodard has one and the machining is first class. Yes the action and barrel are also important and Bat makes an action that is pretty cool once loaded you lay another round on the top of the action and when you open the bolt the spent casing is ejected and the other round drops into place and you just close the bolt and lay another round on top. I can't speak to the Magnum Metal rails as I don't recall seeing or shooting next to one, my current rail is a Hasecuster, and shoots extremely well.