From what I understand in the 64MB versions the memory <i>is</i> higher quality silicon (actually the 128MB was given <i>lower</i> quality silicon at a lower speed to keep the cost down, or else it would just be an underclocked Ti4600😀).
I own an Abit Siluro Ti4200 64MB and I have found it will run just about any game smoothly at 1024x768x32, just with no anisotropic filtering or antialiasing. What games are those you ask?
Half Life (and all of its kids), Dungeon Siege, Neverwinter Nights, Serious Sam 2, Jedi Knight II, Unreal Tournamant2003, Unreal 2, Freelancer, Postal 2, Star Trek Elite Force II, Tron 2.0. Man that's a lot of sequels, never noticed until I listed them.
This was on a:
Athlon XP1800 (Palomino)
Abit KT266A mobo with 512MB of PC2100
Maxtor 7200rpm hard disk
😎