Ben Spies was ranked only 15th fastest during Friday practice at Valencia, but set the joint seventh fastest top speed.
The newly crowned World Superbike champion, riding as a wild-card this weekend ahead of a full 2010 MotoGP campaign, clocked 306.6km/h - exactly equal with factory Honda rider Andrea Dovizioso and factory Yamaha rider Jorge Lorenzo.
The highest M1 top speed was 307.1km/h by Lorenzo's Fiat Yamaha team-mate Valentino Rossi, while the satellite Tech 3 Yamaha bikes of Colin Edwards and James Toseland were once again at the bottom of the speed charts.
Edwards set 302.3km/h to be ranked 15th on the speed chart, while Toseland's 300.5km/h left him 18th and last.
Before the weekend speculation was rife that Yamaha might place some 'power-up' or 2010 development parts into the M1 of Spies - since he is not subject to the engine change limit - but Yamaha have publically claimed his bike is very similar to the satellite Tech 3 machines.
The top speed by Spies could of course have been set in a slipstream, with the benefit of a fortunately-timed tail wind, or he could simply be particularly good at exiting the final turn.
However, with the other Yamaha riders all ahead of Spies on overall lap times - Lorenzo, for example, was 1.857sec quicker than Spies over a full lap - the American's top speed is sure to have raised some eyebrows.
Lorenzo was second fastest in practice, Rossi fourth, Edwards seventh and Toseland 13th.
The highest top speed of all was a 310.7km/h by Repsol Honda's Dani Pedrosa, while practice pace setter Casey Stoner was fourth with a 308.7km/h for Ducati.