I also have their signature card, was recently upgraded along with 35k cl... Their CS is by FAR the BEST I've ever encountered. To think... only had a store card back in 09-04 with 1000 cl, Went up to plat visa less than 6 months prior to upgrading to signature.
As for CLs, Started at 1k, went up to 2k, 4700, 6000, 8000, then 35k...
Amazing...