Yamaha leads battle
Yamaha certainly lead the battle on the timesheets as it stands, thanks to Quartararo. But team-mate Franco Morbidelli had some solid speed too, and Valentino Rossi (Monster Energy Yamaha MotoGP) was up there as Sepang came to a close.
His team-mate Maverick Vinales, the man who won the race in Malaysia last year, was not in terms of the timesheets - but he was also pretty positive and did not go for that all-out time-attack lap. Better top speed was something he pointed out, something high on the Iwata marque's agenda.
Cal Crutchlow (LCR Honda Castrol) flew the flag for Honda at Sepang, ending the test less than a tenth off Quartararo. The Briton also took on a huge workload for Honda, on serious testing duty.
With reigning champion Marc Marquez (Repsol Honda Team) - now signed up with Honda for another four years - coming back from shoulder surgery and his new team-mate a rookie in the form of Alex Marquez, Crutchlow had a long list of items to test.
Suzuki, meanwhile, seemed positively brimming for much of the Sepang Test.
And for good reason, as both Alex Rins (Team Suzuki Ecstar) and team-mate Joan Mir showed serious speed on longer runs and single laps. That caught the attention of many up and down pit-lane too - so will we see that transfer into more speed in the desert?
At Ducati, the feedback was more cautious - as is often the case - but Ducati Corse boss Luigi Dall'Igna was fairly satisfied with the improvements they made.
The new tyres were something Andrea Dovizioso (Ducati Team) and team-mate Danilo Petrucci were focused on for a lot of the time - also running in tandem to gain more data.