I don't know what to think, when looking at data from day 1 and 2 (
viewtopic.php?p=814299#p814299 ) it does look like RB/Merc/Ferrari are still two steps ahead of the rest. I'm basing my comments on that spreadsheet, so if it is innacurate, so is my comment. I'm by no means an expert, so take this with a grain of salt (check the spreadsheets yourself)
Merc on Day 1 did a 14 lap stint around high 1:20s (C2)
Red Bull on Day 1 did a 14 lap stint around mid 1:21s. (C2)
Ferrari is a strange one, they do not appear to have a similar run. Their times are all over the place, only run that is similar is day one run on C1, about 1:22 average.
Renault had a couple of 10ish stints on C2 with roughly 1:22 average, and a 14 lap stint C3 with roughly 1:22s average.
Toro Rosso looks very good on longer runs (20ish laps on 1:23s with C2). I think that they did this with low fuel as immediately after they went to a softer tire (C3) and were doing the same times. I'm guessing they took on fuel which offsetted softer tires.
Alfa shorter runs, about 7-10 laps, times are all over the place. Their times usually drop off at the end of the stint.
Haas is not doing any sort of longer runs, almost all of their runs are quick/slow type of runs.
Racing Point is the same.
Williams is not running.
Now, where does McLaren fit in, it's really hard to say because McLaren did not do similar runs to those teams. McLaren did very short quick/slow runs in the morning, and then a 2/3rd race distance sims in the afternoon, but looking at those race sims, Renault seems similar or somewhat faster than McLaren, TR is around there but hard to tell due to probably running with less fuel, rest is impossible to tell but almost certainly Merc/RB/Ferrari are ahead.
Hopefully we get detailed spreadsheet of runs today so we can speculate further.