You should be able to lower it a bit. You can click the CPU-Z validation in my signature to see, but I'm at 4.6GHz @ 1.344V and 1.288V in Prime totally stable (worked at 1.336V and 1.280V, but turned out to not be completely stable). Anyway, you should be able to use ~1.300-1.330V for 4.5Ghz.
The voltage required to achieve any given overclock varies from CPU to CPU, from motherboard to motherboard, from heatsink to heatsink, etc. There is no universal answer, what works in one person's rig and location will not necessarily work for someone else's. That's why hardware review sites spend hours mapping how their CPU samples behave to get a feel of how uniform or volatile each variable is.
Only way to know if you can lower core voltage in your specific overclock is to try it and test it.
I'm using now 4.6k at 1.315V and have no problems in prime95 in 2 hours. Max temp was 65º Can i run this 24/7 ?
Absolutely. I run 4.6 @ 1.344 (reported, Should be 1.340, but that's what it takes to be completely stable for me) and I have no qualms about running that 24/7 (literally, using the High Performance profile in Windows, except when I'm sleeping, then I just put it in the Balanced profile to let it clock down), so 1.315 is just fine, as far as I'm concerned.
Also, Temps are fine too. I run a degree or two warmer because of the extra voltage, myself (with a Hyper 212 Evo).