Near enough to be believable. And remember that the speed Nicehash "sees" is more important than what your miner reports. Nicehash does the payouts, not your miner

Update with data up till now: http://jacob.j-e-b.net/nicehash2.ods

It also contains the raw readings (columns are in pairs, algo0-raw, algo0-calc, algo1-...), so you can try out other formulas. Mine was just "speed = (speed*99+new_value)/100" with a check of "new_value > 0".

Note: Real implementation would need to make sure to not take readings in the 5-minute ramping up phase. You can see the negative effects in my graphs above after each blue spike. It also should use some recover logic, e.g. what I outlined above, so a bad phase does not disable an algo forever.