For 24/7 use I'd have no problem running 1.4v on air keeping max temps under 50*C, even on water I'd say around 1.45v is around max for 24/7, 1.5v would worry me a little. Remember the P45 chipset is 65nm, and 1.5v is pretty much max for 65nm cpu's 24/7, and intel rate the P45 at ~1.2v absolute max, so even at 1.4v it's already over that by a bit- this is why it's hard to advise anyone on a safe voltage as most of us are already over the rated absolute max. Just depends on how hard you want to push it really.