Old systems were made for those Old OS. Thats why those systems run faster on old OS. I have a PC which supports windows 2k till windows 10. Probably it would run windows 11 too. But I chose to install xp on Pentium D laptop with 3 GB RAM. I dont like vista and 7 has already ended its life cycle. It cant run windows 10 making it unusable for online works. But xp runs superfast on it. The copying speed is same as windows 10 though it wont match CPU mark.
I remember a time when the time estimates for completing OS installations were somewhat accurate (and the first text mode part of the install also took something like 30 minutes to complete).
I just did the same with my Toshiba M70 laptop and it took me about the same time wich is very fast compared to the original WU service. I remember ~15 years ago after reinstalling XP, my PC had to be turned on for 2 days just to find and install all I the updates! I'm glad this exists.
But if you slipstream then you can directly upgrade to SP3. But its better to update to SP2 or start with SP2 integrated and then integrate SP3. The only difference is that you are left with few extra files.