Re: deteriorating overclock
Ether bump up the cooling performance or bump down on the overclock.
I also had the I7-920 before my current. It hold op pretty well. No need to rush into upgrading, if you are not hardly CPU depended.
MOBO: Asus Maximus 6 Hero - GPU: Gigabyte GTX 980ti xtreme - CPU: I7-4770K - PSU: Corsair AX760
RAM: Corsair Vantage 2x4GB - SSD: Samsung 840 EVO 512 + LiteOn LCS-256 - Case: NZXT H440