> strip few least significant bits

I'm unconvinced. Doesnt this just replace the need to choose a suitable epsilon with the need to choose the right number of bits to strip? With the latter affording much fewer choices for degree of "roughness" than does the former.

Not quite. It's basically a combined mantissa and exponent test, so it can be thought of as functionally equivalent to scaling epsilon by a power of two (the shared exponent of the nearly equal floating point values) and then using that epsilon.

I think I'll just use scaled epsilon... though I've gotten lots of performance wins out of direct bitwise trickery with floats (e.g., fast rounding with mantissa normalization and casting).