i've been running esxi 5.5 on a dell latitude 6230 and hp 2560, with additional nic drivers added via third part and ftp server.
no problems for me other than needing more than 4gb, i've been running a vm 24x7 for a few months recently for deployment and testing.
5.5 is my staple at the moment while i'm testing 6.5
the 2560 i've replaced the cd drive with a extra hard disk so i can swap between a full os and a hypervisor. to give me more options.
only real thing with 6.5 is the need for uefi.