I'm 6'6" tall and tip the scales at 245 and I can't make the floor bounce in my boat with 1/2" the long. stringers in my starcraft were 18" apart. The original floor was 1/2 and it lasted for 18 years if I get that much service out of it I'll be happy, if you go with 3/4 your probably going to have a tough time fitting the edges.. I also have a 18 footer with only a 50 merc and every pound makes a difference when it comes to w.o.t. speed. While you have the floor up its a good idea to change everything that gets covered by it and redo the live wells etc. I filled every void with blue dow board from lowes also, it made the boat a lot quieter when running.