Big advantage that N9 hardware has compared to most Android phones: 1GB RAM.
If linux likes anything, it's having more RAM. And by likes, I mean, can use properly and have the user feel the difference.

What the N9 doesn't have, compared to recent top phones, is a recent super-GHz dual core CPU.
With the current OS it doesn't seem to need it, but with android it will fall short of phones like SGS2 and such.

It's certainly cool just for the heck of it, but I wouldn't want an N9 with android. I would want an N9/Harmattan device with all Android apps, but if that comes at a performance penalty, then I'd rather not.

BTW on apps, apart from vncviewer (presencevnc doesn't work for me atm), there's nothing I miss on the N9 that I have on my android phone.
And every time I take my android phone to hand, I miss Harmattan...

BTW my now favourite app on N9: marble touch. It will come to android, but for now it's not there, and it's gorgeous even in it's present (very young) incarnation (well, inbinarification, really, and if that isn't a word it is now and I coined it).

Lastly, on hardware comparisons: half the info is missing to make a good comparison, what is know on the RAM interface speed? What is known on the flash speed? Very important when opening apps. How long is battery lifetime when doing certain tasks?
For sure my android phone's battery lasts longer with the N9 close by, but that's not really what I meant...