i would be satisfied with N900*2..
And then the 32GB flash mem doesnt have to follow the *2 rule... ( i am fine with 32GB on board with a SDHC, SDXC would be nice but i guess that exFat problem will not help..)

so,
dual core,
512MB ram (i think that would work fine for me looking to my current ram usage, 256 is just to little)
512MB rootfs instead of that 256MB but 1.3 did fix most of the problems for me in this area, but the larger this area is the faster the phone because this is the fastest flash there is on the N900..

But dual core is for me a must, the N900 is sometimes just to slow because i do multiply things at the same time... Don't think i will buy the N9 if it is still a A8 on 1Ghz, that wont be much faster then my N900 on 900Mhz.... (or the ram must do a lot)