the goretex vs softshell opionion must be based off personal experience of severe downfalls of said material. you should really try the new proshell if you get a chance, it really makes up for the pitfalls that brought about the softshell revolution.
The gamma mx jacket I saw was not powershield or anything close, it was a featherweight jacket..thus the amazement that this garment would the a coveted winter piece. REI must have put the wrong label on. If it's anything like the Mammot Champ jacket or older Gamma LT, then I'm sure it's quality. If however, this suposed Gamma MX jacket is what you guys are talking about, you must be nuts or brainwashed by hype -