Game plays worse/slower in newer versions: Is this considered regression?

[Rekrul]

I haven't played Midnight Club 3: Dub Edition in a while. The other day I loaded it up in 1.8.0 and noticed that the game was stuttering and randomly slowing down, even when set to 1:1 resolution and only 2x filtering. I thought this was strange as I don't remember it having any problems on the same system in the past.

So I went back to 1.6.3, which was the last official release I was using and the game runs silky smooth. In fact, I can bump the resolution up to 4x and put the filtering on 16x and it still runs better than 1:1/2x do in 1.8.0. The main menu runs worse and the sound stutters there, but the game itself plays perfectly.

I tried to isolate when the slowdown started, but after testing a bunch of versions, it just seems to be progressive and hard to nail down. Sometimes it will slow down/stutter, sometimes not. The only consistent factor was that each version I tested after 1.6.3 seemed to be worse than the previous version. The random slowdowns would happen more frequently.

This is in the Windows 32-bit version running on;

2.4Ghz Core-2-Duo
GT430 graphics card
4GB RAM
Onboard sound
Windows XP SP3 (yes, I know it's outdated)

Would the fact that later versions have trouble running this on the same hardware be considered a regression, or would it just be chalked up to later versions having steeper system requirements than older versions?