Throw lever in this system is definetly superior to the screw mount. It's faster on and off and won't freeze up requiring a screwdriver to loosen.
If you go with the pressure pad might I suggest you hit the uppers/lowers/barrels/etc. forum and check out SMGLee's recent posting regarding the tango down grip. It's capable of accepting your pressure switch inletted into the grip's side and I believe will accomodate storage for spare batteries.
Oh, and I might add for both of you, gunshows are really a good source of Surefire items. There were several dealers at the Tulsa show this weekend, not only will they have competing prices at shows like this but you can get hands on examination with all these units prior to purchasing. That way you can half way evaluate the weight increase it will add to your system and any balancing issues.
A good example of this is I'm running an M900A verticle grip light, I've seen prices up and down on these units online, but picked mine up brand new for $400 off a dealer that had special ordered it in for a customer who never paid him or picked it up.