Both choices (Rod Rainier or Gunnar Fast Lane) are super nice. It seems like you're really inclined in getting disc brakes which either Rodriguez or Gunnar can do. One of your choices (#6) is a bike with a belt drive system. Is that something you see yourself having or adding in the future? If you're thinking of adding a more sophisticated belt drive or Rohloff, then the guys at Rodriguez win hands down, IMHO. These guys have tons of expertise with eccentric bottom brackets (EBB) and special rear dropouts which are needed for these more sophisticated systems. Very few builders have this kind of expertise and if they do, they really overcharge. Obviously, they can put a derailleur hanger (parallel with the EBB, Rohloff or belt stuff), if that's all you want for now. I did this recently with a Rodriguez UTB which is more of a hardcore touring bike. You can see more level of detail
here. In regard to Reynolds 725 steel, it is top-notch steel that offers a tad of flexibility. It makes them feel really nice (compliant!) on the road. Frames that are too stiff don't feel so good, especially if you're going to be riding with light loads: CC touring, commuting, long ride on Sunday with your buddies. They offer steel upgrades to True Temper Platinum OX or Stainless Steel which people also rave about. The stainless steel options I've seen these guys build look like they truly kick a*s!
If you're just going for a simple ole good derailleur drivetrain, it's a toss-up between Rodriguez and Gunnar. When selecting a builder, it might be a good idea to send an email letting them know you're in the market for a new frame (or complete build!) and they are one of your top choices. State your purposes for this frame. I personally also like to include a couple of tough questions (or concerns) and see how each builder responds. You definitely want to see how promptly they reply, their level of know-how, etc. Basically, you need to feel warm and fuzzy working with a builder at this level to insure they're going to meet all your needs.
Keep us posted!