If you get the larger sail, you can still use it just fine on a 110-115 liter board.
You can get a wider 110-120 liter board that will plane significantly earlier.
Almost any > 100 liter board can be used with your 5.7 m2 and 7.5 m2 rigs, and any board > 115 liters (and fairly wide (I.E. > 75 cm) will work with all of your sails, abeit better with the 7.5/8.5.
For > 20 knots of wind, you would need a smaller board and probably could sail up to 22 knots with your
5.7 well tuned for high winds.
Sounds like you need a smaller board (you are light in weight @ 155 lbs.) but the normal range of your windspeeds is >10- <20 knots which suits the 110-125 liter boards prefectly.
Also suits you sail sizes for an advancing sailor. Might want to pick up a good 6.5 m2 at some point as there's a bit of a gap from 5.7-7.5 particularly is the 5.7 is a freeride sail and the 7.5 is a free race sail.
Hope this helps,