The confusing world of the slow, lagging Nokia N97... and a surprising little speed fix!

I have previously written a lot about the Nokia N97, it's ups and downs, features and frustrations.
Of late though, my trusty N97 has become unbearably slow - lagging to the point of ultimate frustration.
Random restarts do not really make the experience any better.

So I decided to take the plunge and hard reset the damn thing - for those non-techies reading this, a hard reset is essentially the same as a PC reformat - a complete wipe of the system drive, and a restoration to factory defaults.
It is usually the best way to restore a device to former glory.

So after a meticulous backup of all my data, I did the hard reset and held my breath...
Initially the process seemed to have worked - swiftness had returned!
... for about 5 minutes, that is, and then... return of the snail.

Next I tried a soft reset - which does not erase your data, but restores phone settings to factory defaults.
Same result.
So after both a hard and a soft reset, I resigned myself to a slow phone sometime during the day yesterday.
Not wanting to return the handset to Cell C again, I pretty much told myself to just live with the slowness.

Then last night I was checking the contents of the phone's internal 32GB memory, and I found about 10GB of data that I no longer need.
Wanting to keep space available for photos, videos and music, I deleted the 10GB as my 32GB was down to about 3GB free.
Miracle of miracles - this morning the damn thing is lightning fast again!

No more lagging while typing.
No more lagging while scrolling through lists.
Minimal waiting for apps to open.
No restarts (yet...)

So is this an undocumented little tidbit of the phone that Nokia have failed to pick up?
To my knowledge, the phone's performance is affected by free space on the C: Drive, not that of the 32GB onboard mass memory...
I am keen to find out if I am the only one who has had this result - if you are a Nokia N97 owner with a laggy phone, and your 32GB onboard memory is nearly full, try freeing up 10GB+ on there, and see if it helps matters...
Comments and feedback are always welcome!