@ WebMaximus
Since that is a default option, I would leave the 'Speed up scanning by using the persistent cache' option checked (enabled).
I have systems with HDD and SDD hard drives as the primary drive, but the way I see it with an SDD they are less prone to the hassles of location as in an HDD drive. But I can't see that hurting if it is enabled, after all SDD soft/firmware would be placing files to prevent/balance writes to the SDD. I also don't know how much impact TRIM would have in relation to that setting.
But this XP Pro system has HDD as the primary so I would probably get greater benefit from that option.
If you are running these scans at a time when you are using the system, it is going to be slightly hampered even if set to High priority. After all I thought that was the point of scheduling scans. That said some are reporting issues with scheduled scans starting as per the schedule.
I certainly feel a robust backup and recover strategy would be a better way to go.