Right, so let's summarize:
Arrow I: 111 mph (96 kt)
Arrow II: 105 mph (91 kt)
Arrow III: 79 kt
Arrow IV (turbo): 97 kt
mcgoo is that an Arrow IV with a turbo? If not then it appears that the non-turbo IV matches the III which would make sense. The Arrow I and II share the same 'hershey bar' wing while the III and IV both have the tapered wing. But that brings up the question: why would bolting a turbo to an engine change the glide speed?
As for weights (MTOW), I don't have the Arrow I POH but for the others:
Arrow II: 2650 lbs
Arrow III: 2750 lbs
Arrow IV (turbo): 2900 lbs