It is possible that the SP3 you used for comparison was somehow corrupted.
On my hardware, SP3 was indeed "faster" than SP2.
I am not a "gut feeling" type of guy. I took quantifiable and repeatable measurements that led me to using SP3 over SP2.
Hard facts that were repeatable. No "gut feeling", no "placebo effect".
That's not to say that you are "full of it", lol, it is POSSIBLE that SP2 is "faster" on your hardware. Just saying that was not the case back in the day when I compared the two.
One POSSIBLE factor is that I *never* install a Service Pack 'on top of' an existing installation - I SLIPSTREAM IT INTO MY INSTALLATION DISK. Then FORMAT and INSTALL brand new.