Phenom II X2 550BE. 3rd core unlocked, 3.3ghz @ 1.31v Replace
That's an 80W CPU that you've seemingly overclocked. In coarse TDP figures (which is used for cooling, not necessarily a representation of power draw*), it likely exceeds the i5-4570 at 84W TDP. However, the actual power that the i5-4570 system would draw on average is likely much
lower than your current setup due to chipset efficiency and much lower idle power. All this is without considering the 6450 in your current rig (27W TDP) that isn't needed for an i5 system. "S" series CPUs aren't worth the extra cost IMO, as Duct Tape Dude
pointed out, you can always lower the TDP of an i5-4570 through either voltage and/or multiplier reductions in the UEFI (underclocking) or TDP adjustments in Windows software utilities. I know Asus has a handy Utility for this (see Video 3 here @ 7:10
Also, this article
might help debunk any misconceptions of "low-power" CPUs. Basically "S-series" parts aren't really any better than regular(?) ones. "T-series" gives you lower power draw and temps at a given moment, which is good for enclosures with severely limited cooling capacity, but they require more total power to complete a given task than a regular i5.
I second the vote for the Z87 Gryphon.
* Intel's TDP figures seem to roughly match system power draw
(i4-4770 also has an 84W TDP) while AMD seems to use some other math to figure it's TDP.
Main: i5-3570K, ASRock Z77 Pro4-M, Asus GTX660 TOP, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod