Thanks for the suggestion however it really is cheaper the better, both up front cost and electricity costs. I think the ND22 would be easily powerful enough with 4GB RAM and if I can get it (and certainly the ram/HDD) second hand that will save me a bomb!
Thanks for the SPC review, I'll peruse that now. I guess noise won't be too much of a problem if I stuck it up in the attic and remoted into it depending on ease of use...