AMP 8 sizing guide is below, the table is different than what you have but it is a small measuring stick to what you should be looking for.
I have an Airwave running 8.0.0 monitoring 532 devices. I was just fine on 7.7.x, after upgrading to 8.0.0,
I have some performance issues and disk space issues.
My server is not as performant as the ones indicated above ( we are in the process of upgrading the hardware).
It has 16Gb of ram with a a 275Gb HD and an Intel(R) Xeon(R) CPU E31220 @ 3.10GHz 4 Cores 8192 KB cache (3093.100 MHz actual)
After upgrading a few weeks ago to MAP 8, just now I am starting to run out of diskspace, granted I can tweak historical data retention and run reports, etc..to reduce the disk space usage.
I see also between 4000-5000 clients a day on this machine.
I think from this you can judge what kind of server you need. RAM is key and if you want to keep as much data as possible on your server, then get lots of HD space.