TShad succumb to cold water at about 42 F. A 5-6 in. shad is about right for an adult TShad. GShad could be that size but they get much bigger like 12 in. I think Bill posted that some up north get 18 - 19 in. . FishBase reports GShad to 40cm = 15.72 in. Yes GShad get to big for all but lunker LMB to eat and they have IMHO other very negative aspects as well in ponds.

http://www.fishbase.org/Summary/SpeciesSummary.php?id=1604 GShad

http://www.fishbase.org/Summary/SpeciesSummary.php?id=1606 TShad