I have to say, I'm on
IBB 1Mbps ADSL, and they've been pretty much spot on. Don't forget that wireless is inherently unstable - you're relying on line-of-sight and good weather conditions, and are subject to other RF interference, so you won't always get the best connection. Also, the further you are from the tower, the slower your connection will be simply because the signal dissipates as it travels away from the mast.
I was on Ripwave once. Despite getting full signal strength and quality (5x5, as they say), I couldn't even connect. In short, stay away from Ripwave!
However, this site and others like it are pretty accurate with their calculations. If
IBB are trying to tell you that any online speed test is wrong, they're leading you down the garden path…