Carlos Sainz kept McLaren at the top of the timesheet on Wednesday, but the Spaniard is under no illusions that Red Bull and Ferrari have the potential to beat his benchmark time.
Sainz picked up where team mate Lando Norris left off on Tuesday, posting the fastest lap so far in pre-season testing at the wheel of his C4-shod MCL34.
Despite the impressive performance, Sainz insists McLaren is targeting more progress in the final two days of preparation.
"The important stuff to come out of this seven or eight days [is that] I think every time I've been on track the car has been progressing," he said.
"I think our car balance has gotten better over the last few days, and that is allowing us to extract a bit more from it.
"But still there is a long season ahead where we need to keep working, we're still not where we want to be.
"This is definitely the right answer, and we need to keep working hard because a [1m]17.1s around Barcelona is fast I guess, but I expect teams like Ferrari and Red Bull can go much lower and much faster than that. So I'm very cautious and very calm."
As is the case for most teams, McLaren's MCL34 is a work in progress, and Sainz underlined the changes the car had undergone since its track debut last week, with more modifications in store.
"Pretty much everything has kind of been improved," he said.
"There's still underlying balance issues that we are working on and that we cannot get rid of until we bring upgrades to the car.
"So that's what Formula 1 is about: decide on what you need to improve, and in the following races try and bring upgrades to make it a bit better."
While McLaren's performance has been positive, its overall mileage in pre-season testing has been limited by small reliability issues. But uncovering and solving teething problems is the very reason why a team goes testing said Sainz.
"Every day you'd like to do a couple more runs, but that is what testing is for," he said.
"Because if you don't find the reliability issues in testing like we are finding now, than it means that you're not covering enough work.
"We're finding issues, but we are solving them and we are getting back out on track like today and we did 130 laps with a couple of issues. So that's good news and good progress."