I'm trying to figure out how good my props are on my 1997 29 fever with twin 502's. I just finished rebuilding the motors but want to see if the props are good to keep or should I try to send them to BBLades and have them tweaked a little or get new.

I bought the boat with the props so never really knew much about them.

Here is what I was running before the rebuilds and the speeds are accurate as far as I know. GPS on my boat and many others that have confirmed.

5000rpm 78 mph and 1.5 drives. running Hydromotive Q4 26 pitch. This figured out to be 4.96% slip on BBlades calculator. Is this possible?

Is this correct and if so is is it too low or to high for slip? What do you all think?

It is possible but also unlikely.
9-10 would be excelent and more reasonable.
If the boat gets on plane well and carrys well your in a great spot.
The next move would be something like testing 28 Bravo 1's to determine if Labbing was a possibility.

Brett