If you split an 'Atom' ...
Then you get just half of the some pretty bad FPU performance.
The 'Atom' has less FPU performance than the crappiest Celeron you can still buy .. oh but it uses 5% less power. The VIA C-7 doesn't look so bad anymore, and the New VIA Nano/Isaiah even beats the 'Atom' in early benchmarks.
ARM sounds way better to me, then again I don't care for windows. And don't let the low mhz numbers fool you, ARM can really perform a lot at low clock speeds. Anyone who's ever installed Linux on an NSLU2 can tell you that!