It seems to perform about the same for the most part. The only big difference I have noticed between the 2 is that SoF seems to send you back to the login screen quicker if you get disconnected for any reason instead of leaving you on a "disconnected" screen for 3 minutes or so like Titanium does.
I have also heard that SoF has better multi-core support so people wouldn't run into the dual core issues as much as they do with Titanium. But, on Vista, that shouldn't be too much of an issue. Though, I have heard that it helps with the multi-core issues some on Vista as well.
I think it has a few more new effect settings that you can enable in the advanced display options screen. It still looks mostly the same, but maybe a bit better on some things.
One odd thing I have noticed with the video on my system is that when you load into a zone, it seems to paint some of the textures onto NPCs after you finish loading in. So, for a second after zoning or logging in, you might see some white or grey parts on some NPCs, but then it changes to normal in a second. As far as I can tell, it is doing that to help performance, but I don't know for sure. My best guess is that it is trying to only load textures when it knows you are looking at them.
SoF is only enabled on a couple of servers (that I know of) right now. So, you wouldn't be able to use it on all servers. And even on some others that might have it enabled, they may not be current, which is important, since alot of fixes were put in lately. SoF is very functional and almost complete, but the best functionality is still from Titanium. At least until we get AAs fully functional (many already work), and maybe a couple of other minor fixes in.
As I have said many times before though, I would recommend getting SoF right now. This is because
www.newegg.com has it for 4.99 with free shipping and that is a very hard deal to pass up. Much better to get it now at that price than to wait until they run out and have to pay more or have trouble finding it at all. Just something to keep in mind, but $5 is really a pretty small amount considering how much use you could get out of it.