Intel x86 N900 co computer side
Self made Intel edison seems to be faster and smaller than a n900 or a pi.
It can run a ubilinux http://www.emutexlabs.com/ubilinux. (debian "Wheezy", on 3.10 kernel).
(But self made self powered is not easy due to several design flaws.
https://learn.sparkfun.com/tutorials...-battery-block and slow charging times http://www.helios.de/heliosapp/edison/)

If you want a more powerful device you can take an
Intel compute stick (sold with Ubuntu) and a a large powerbank battery.
Someone flashed ubuntu even on the larger 2 GB Windows version.
If you up for flashing and a little porting challenge you can try the more stylish
Ainol Mini PC:
http://www.ainol-novo.com/ainol-mini-pc-black.html
It seems it is just a compute stick with a large powerbank.
or [Voyo (similar):
http://www.cnx-software.com/2015/02/...0-mah-battery/]

Could be a great expansion for the a N900. Where you "tether" your network, keyboard and display and leave the "big" server in your pocket.

But they all need some tinkering on the software side or even hardware side and even worse are Intels

(Maybe invest 800 Euro in porting ubuntu to a ainol or voyo)

Or build your own based on a fast arm (raxda, odroid, olimex) som and a large powerbank.

Or a more geeky zynq device (arm cortex a9 and fpga)
https://wiki.trenz-electronic.de/pag...ageId=20612048
sadly only 64mb ram and not released yet..