5 i would say is to small if your trying to deep water, even with a tav, i have a 7.5 hp and it can deep water start people no problem, but anywhere we winch, we just use a plastic chair, way easier. i would go at least 7.5. 7.5-9 is ideal. my friend has a 9 hp winch, and its a torque machine, it has a speed sprocket on it, and it deep waters people that weigh around 250 and can still pull over 24 mph.
another big factor, is how fast do you want to go? that can be adjusted with sprockets, and the spool diameter, but with a fast sprocket, you will lose torque. so you need the motor and sprockets to work together for your desired needs.
i have my govenor adjusted so full throttle pulls a wakeboarder about 22. thats about where all my friends and I hit rails at. it pulls you on a wakeskate MUCH faster though, half throttle is plenty fast.