I just configured two 365 X 24 servers — MacBook Pro 13" (June 2012) 2.9 GHz. Laptops like the MacBook Pro have been rock solid for me running 24 hours a day for years.
I wanted 16GB for my purposes (a need, not an option), and the 6G SSD makes things like a git server run without delay, at least on the local network.
The 13" MBP is only dual core, but at 2.9 GHz, they “rock” for most things. And bought refurbished, one can save some money.