I live down in Sugar land and have ridden with SWCC a couple times. The group is good but even with the "B" group we took a pretty high pace. I think it probably averaged about 21mph but good pacelines. I think we did about 50 miles, it has been a while since I went with them.
I usually do rides in Houston rather than from my house so I don't know those areas as well. My averages are probably closer to 17-18mph now (too lazy).