Have you thought about ditching the rack and going with a seat bag like the Caradice Long Flap Nelson or Camping bag. They are right up your alley for credit card touring. They are nice looking, tough, hold a significant amount, are used by a few for longer trips, and there is no heel strike. You can also mount a small support rack to your seat post if you plan on filling the bag heavy. I use Caradice Super C panniers and love them. As suggested above check Wiggle or Probikekit for better pricing and shipping deals. I bought mine from Wiggle for much less than I could ever get them here, and got free shipping.