yeah ...it should be powerful enough but...
I would seriously consider having a keyboard, as Sonar is so keyboard-centric...
and that new Metro, and whole new app-centric M$ is going to with tablets somehow scares me..
and while having a tablet with a keyboard, why not have a laptop ?
Sonar X1 does not like touchscreen too much (faders does not work well with touch)
X2 promises to fix that (once Windows 8 is out so I red here on the forum).
So a 11 inch macbook air with Windows 7 might be an interesting solution.
or as you liked HP, they also do a 12 inch elitebook that has a up to a dual core i7,
(and are more equipped in IO than the macbook air)
Dell also has pretty slick little laptops that sometimes go for very little money when the right sale occurs. I just bought a 17 inch Vostro with i7 to run Sonar on, I returned a HP for this one, and do not regret it.....
Cheers!
V