Dell 9560 mainboard replacement - now it's fast again

Today I had my mainboard replaced under warranty on my 2017 Dell XPS 9560 (15"), reason being that the wireless card screw post had become physically detatched from the mainboard and was rattling around inside. This was a very recent problem, but I've owned the laptop for over 3 years.

However after my mainboard was replaced, my laptop now runs noticeably faster.

Over the last 2 years of owning the laptop, I've noticed it has been really laggy, taking 1m30 to launch Adobe Lightroom, sometimes delays of 10 seconds to open a Windows explorer window, etc. There have been no major hangs where it just freezes altogether (at least no more regularly than I'd expect with any machine running Windows) but definitely an issue with general slowness.

After the replacement, today Lightroom launched in a matter of seconds. I was able to browse through a large photo database with ease, no delays zooming in 100% on photos etc. Exactly how it should always have been.

About 6 months ago I had become frustrated with the slowness and rebuilt Windows from scratch. I noticed there was a process called "System Interrupts" which ran at 100% CPU usage sometimes, and after researching this online I understood this to be a driver based issue.

My question is this.

Clearly there has been a problem with the hardware, that the diagnostics had not picked up. Maybe it was a thermal issue (fans, thermal paste, heatsink), maybe a graphics hardware error, maybe something else.

But could I have picked up on this with some software? Is there some way I could have known that performance was being throttled, if indeed it was a thermal issue?

Or is there some application (I don't think standard benchmarking would work) that could have indicated a problem?

What if the laptop gets slower again, over a long period of time, such that I don't notice? How can I measure this?

For reference, here's the spec on my XPS:

• 1TB PCIe Solid State Drive
• 32GB (2x16GB) DDR4 at 2400MHz
• 15.6" 4K Ultra HD (3840 x 2160 ) InfinityEdge touch display
• 7th Generation Intel(R) Core(T M) i7-7700HQ Quad Core Process