Have you seen this thread?

http://ths.gardenweb.com/forums/load/appl/msg031038102055.html

Dealers can order an RCS as well, just like the one at Costco. Some things, like a convection fan may be optional on the RCS.

The one thing they don't upgrade is the larger burner. And I was told years ago that the stainless gauge was thinner on the RCS.. the other differences are listed on the link above- ignition, drip tray, rolling oven trays etc.

Still the RCS is a great value.

Here is a link that might be useful: link to earlier discussion

The link provided by alexr may be useful to you -- some good points raised there by both RNB and RCS owners.

I'm very happy with my RNB, and would gladly do it all over again, but the RCS seems to represent good value for money, especially on some of the special Costco deals I've seen posted. Some specs are different between the ranges, and you can decide how much that matters to you, but I've never heard that they build them anywhere else, or to a different level of QC. I suspect, rather, that Costco has negotiated a good price on a particular lot -- they do that sort of thing -- and that it's being disparaged by a salesman who is either passing along an unsubstantiated rumor or being . . . er, creative.

Italianchef - did you decide to get the Costco Bluestar RCS?

I ended up phoning Bluestar about what the non-Costco dealers are saying about (dissing!) the Bluestar sold by Costco: it was most enlightening, and I encourage you to do the same, if you haven't made up your mind yet.