well I'd like to direct you over to a thread about the difference between the Cintiq and Tablet Pc on the RESULTS of thier pressure sensitivity
*most* tablet pcs come in at 512 levels ... the 256 is on models older than 2004, as my m1400 made in '04 comes with 512 and it works great.
and personally, having settled with great satisfaction on the 4 year old M1400, I can only predict that you can't go wrong with ANY new models ... just make sure they use the Wacom tech, and not other tech.
There are even some people who have put touch sensitivity and the Wacom on a single tablet and switch out using a software setting.
I hope anyone else who has good info will pitch in their 2 cents for you as well.
and keep on asking as many questions as you have