[progers7]

SMIL is not perfectly fluid. SMIL is not inherently hardware accelerated. SMIL animations are slower than the same animations driven from JS in all major browsers except IE which doesn't support SMIL but does support JS. As the OP showed, JS animations are the way to go for SVG.

[squared9]

My experience says otherwise, SVG SMIL tends to be 10-20% faster with lower CPU load in recent browsers (Chrome/FF/Safari) than a JS-driven animation. YMMV though.

[ygra]

One might argue that an animation that doesn't even play is infinitely slow ;)