tl;dr you could probably fit around 32GB-48GB per E3-1230 as long as you're not selling ridiculously low memory vps like 256MB. Just make sure your RAID array will be able to handle the I/O load. 4x250GB with a HW RAID card and BBU/NAND cache and you should be golden. The more drives the better, though.
If you don't go raid-10 you're basically shooting yourself in the foot and you can expect even less then 16GB a node. RAID-5 is okay but it actually is worse then a raid-1 array when it comes to write performance. So needless to say if you go raid-5 expect less then a single sata 7200 in regards to write speed -- at least on small writes, anyway. Larger ones tend to be little better.