I don't know about GBR, but I do have white clouds. I looked at the fish profile for both using the link at the top of the page, and they do have an overlapping temp range. The GBR has a really narrow range and the WCMM have a wider range, but temperature wise, they would seem compatible. The WCMM would be living in the top degrees of their recommended temp range.
I love my WCMM. They are neat little fish, they school nicely. I have the goldens, but there is also a longfin version that I am interested in.
Since it appears your GBR has a really narrow range of acceptable temperatures, I'd look for fish that overlap that requirement.