The Italian outfit has battled with a lack of consistency from its SF-23 throughout this season, especially in races when its drivers struggle with a lack of confidence because car handling is not predictable.
Upgrades to the car introduced since the Spanish Grand Prix have helped improve matters considerably, and both Sainz and Charles Leclerc were left bullish after last weekend's race in Austria where further updates arrived.
However, Sainz is still remaining cautious about just how much of its problem has been solved so far and thinks the British GP weekend could be hugely helpful in delivering a clearer picture.
Asked by Autosport if he felt the corner had been turned on car consistency, Sainz said: "We don't know. I think we need maybe a more open windy circuit like Silverstone to evaluate it.
"Normally, we've been struggling more in windy conditions like Miami and Baku, and in the race sometimes. So, I think we need more samples to assess our progress and our upgrade package.
"What I can tell you is that the car felt better in Austria, both over one lap and in the race. But we were also very quick in Austria last year. So, I'm still being cautious and letting the circuits and the season go by to analyse it.
"But I'm proud of the way the team reacted and the amount of upgrades that we've been bringing recently."
Leclerc agreed that Silverstone would be valuable for Ferrari in helping it understand whether or not the recent car changes have delivered what was needed.
"I think since Barcelona really, the feeling is going in the right direction," he said. "We couldn't really prove it at any other tracks since Barcelona, but in Austria, the feeling was good, and the pace was a bit better than what we had for the first part of the season. So that was good.
"I think it shows that there were some steps forward made. However, we shouldn't get carried away. I mean, Red Bull is still a lot in front. And I think this track this weekend will expose a bit more our weaknesses.
"So, we might struggle a bit more than what we've seen in Austria. But it's clear that the feeling and the pace is a step better."
Barcelona breakthrough
Sainz says that ever since the Spanish GP, Ferrari has at least had a better idea of which direction it needs to focus its development.
"In the [Spanish GP] race weekend I did test a few things in the car that allowed me to understand a bit better where our weakness was, and how we could assess it," he said.
"It gave us a pretty clear direction on where to develop and I think that's paying off now. We are on the right track I'm pretty sure.
"Have we turned the corner? I want to believe so. But as I said, we need a few more samples, and we need a windy weekend maybe to assess, even if it means we will struggle a bit more in these conditions."
Additional reporting by Matt Kew
