Be Careful
There's very few posts on this website that give me a shiver, and this is one of them.
"Airspeed off the peg" should be part of every take-off roll cross check. You should also always have an abort plan if things don't look right. For me, if I don't see the anticipated RPM, MP, airspeed, oil temp, and oil pressure with at least 2,000 feet remaining, it's Throttle - IDLE, Brakes - Apply.
If we were talking about heavy aircraft, there would be a specific point after which you have no choice but to take the plane into the air and figure it out on downwind. But our airplanes don't have V1 and S1 speeds, so if you have enough runway left to bring the airplane to a stop, you ought to be aborting.
And whether or not your Operating Limitations requires a functioning airspeed indicator, I can think of all kinds of scenarios where you could be high power, low airspeed. That's why we practice power-on stalls. And GPS ground speed is no substitute. If you have any kind of tailwind and are trying to figure out your airspeed, your GPS is lying.
I certainly don't mean to call anyone on the carpet, but the casual attitude of this conversation has made me nervous. Please, please, please, have a plan for what's going to happen when you push up the throttle and things don't go as you expect. Decide ahead of time when you're going to abort and how. Have a plan for when the engine fails on takeoff. At what point will you land straight ahead and at what point will to attempt to turn back? Run through the steps in your mind each and every time you're about to take the active runway. Expect something to go wrong. Be surprised when it doesn't.
Having a plan and being proficient at it is free, and it might save your bacon.
-Martin
402BD