Well, from what comparisons have been made, the Slim is so far more efficient and better at cooling.
In fact, you'd have to worry less about the system over heating, and more about the disc tray wearing out, which, considering each system comes with a HDD included, is unlikely to ever happen, due to it most likely being installed.
So yeaa, there should be no concerns at all, really.
Server = Remora - Rank 10 Windurstian
75 BLM (Main)
25 SMN (Future Main ^^)
ZM Complete - CoP Complete - Windurst - Complete
LS - Dragonflies