Are you thinking of the 64 meg card or the 128 meg card?
I haven't seen any reviews of either card in the 128 meg variety....but I've seen some write-ups of the 64 meg MSI card and it looks like a great overclocker. Most people seem to be nailing 300/600+ with the MSI which is a nice 20% overclock of both core and mem.
The MSI card also has a really good software bundle including the full versions of No One Lives Forever, Sacrifice, and Aquanox.
If you've never played NOLF I'd recommend the MSI card for that game alone.
I think when it comes right down to it, all of the Ti4200s are very similar to one-another and, since there's never a guarantee with overclocking, your decision should come down to price, software bundle, and extra features.