Mike,
I live and fish near Lake Hopatcong, I assume a 640LX is 16' ?
Not sure if it's to small or not, but there are some BIG boats on Hopatcong and could get very rough, I owned a 2004 ProTeam 185 with a 60hp. The 185 is 18.5' long. Actually my maiden voyage was in Greenwood lake. When Hopatcong was empty the boat was good, but on a busy day, I felt like the 185 with the 60hp was too small for the lake, same for Greenwood.
I know someone selling a 19' 1989 Gambler with a 150 hp in South East PA, if your interested let me know, I could put you in touch with this person.
CJL