It's buttery-smooth for me on IE 10 (not yet on Win 8.1, so I can't check th fps in the dev tools), jerky (< 30 fps) for both PNG and SVG in Chrome (with PNG being actually slower) and very jerky for SVG on Firefox.
Chrome is puzzling and suggests that there are other factors at play that result in poor performance here.
SVG rendering should properly be paired with proper use of the dejeur hardware accelerations of choice, and for that I'm personally finding various fringes of the MOAI community of much interest, as it puts SVG into a fabulous playground.
That's a fairly extreme outlier, though – other than font/icon preview pages, how many sites want to display hundreds of different icons in rapid succession?
In my experience, you can see noticeable performance losses pretty quickly on mobile devices in as few as 9 on-screen icons, especially in cases of animated elements.
Look at it this way, everywhere on your screen you see repetition is an opportunity for a new, simple symbol that can be represented with fundamental glyphs.
