This is what we do (we being a scheduled carrier flying the A319, 320 and 321):
On receiving the preliminary loadsheet at the gate, we work out the take-off speeds for a weight 800kg in excess of the preliminary loadsheet weight. When the final loadsheet appears during taxi, as long as the actual weight is less than our estimate + 800kg sum and the trim is almost the same, we leave all the figures input into the FMC as they are. Obviously, if the actual weight turned out to be more than 800kg more than the estimate, we would calculate new speeds but I can't remember that happening.
It only takes a few seconds to compare the new data with that already input so the risks of being distracted during taxi are insignificant. In any case, at our base you almost never get to the runway without having to stop at least once so there's plenty of time. I can count the number of times we've had to prompt someone for the final loadsheet on one hand.
I doubt it would be much safer to do it at the gate; there is always plenty going on in the last few minutes before departure and that can be distracting too.