Thanks to everybody for their inputs!
Ok to summarize what I think I have learned is:
1) Northern BG can live and perform well in both the South and the North. CNBG are less tolerant to cold temperature than the Northern BG.
2) There is no significant advantage in size or growth rate between CNBG and Northern BG.
Conclusion is there is no advantage in trying to inject some CNBG genetics into my Northern BG and it might actually be a detriment from a temperature tolerance standpoint.
Guess I will forego stocking any CNBG