I believe the M6600 has a 17" screen, while the M4600 has a 15" screen. Suggest looking on Arrow's eBay site (or other) for more detailed info about specs and perhaps better price.
http://www.elitetrader.com/et/index.php?threads/the-mini-desktops.293594/ I would get an Intel NUC link on above thread.
I didn't even know these existed. Thank you for the link. I am disappointed that they put such wimpy cpus in these NUCs.
Very nice deal as for me, yes you really can upgrade ram to needed naximum amount as well as you can really upgrade SSD for something like that for sure as well as something like Windows 10 64 bit should be installed today for your setup really.