A lot of users also note that their phone runs a lot faster when plugged in, or on Sundays, or after their favorite team wins.
Please provide some actual technical logic for the phone to run faster. Just reading it somewhere does not make it happen. By this rational, the phone should run REALLY REALLY slow if you remove your SD card. Nope, phone runs the same without any SD card.
I would bet that those "lot of users have reported less sluggishness when upgrading" was actually because to upgrade their SD card they had to REBOOT the phone. So none of their crappy applications were running to make the phone sluggish.