Hi Graham,
If you imagine (albeit a classic cliché) the aircraft in the sky, as a boat in a river.
If your engine is not running, regardless of the flow of the river, you will be going at 0 m/s in relation to the water. You may well be travelling at say 10 m/s in relation to the riverbank (or ground) if there is a fast flow.
If you relate this directly to the air, at a constant power setting you will travel (assuming weight, altitude and temperature e.t.c. are all constant) at the same airspeed (CAS/TAS), regardless of the windspeed.
When you bring wind into the equation, you are affecting your speed over the ground, not your airspeed - so you may end up at your destination faster or slower, but the speed through the air will remain steady.
The airspeed you read in your cockpit, is the speed of the aircraft through the air - your 2300rpm will always (again, assuming same W.A.T) give you the same airspeed (and therefore an expected performance) which can be used as a ballpark figure to work with over and over again.
What you don't have on a conventional cockpit layout is a ground speed reading, for this you need to then factor in the wind. But again, unless your bothered about what time you get somewhere, this isn't really an issue - your performance is reliant, amongst other things, on your airspeed.
Hope this helps,
Dead Side
Last edited by The Dead Side; 15th Feb 2013 at 13:03.