Well MSI Afterburner does allow overvolting
It's in the settings for afterburner, you just need to enable voltage changing. I'm using a Diamond 5850 at 950/1205 or i can run it at 1000/1205 (it's to hot under full load at 1000/1205). My 950/1205 was running at 1.164v.
What you are talking about doesn't seem to exist, it is practically like AMD Cool'n'Quiet, but yea, it doesn't exist.
This is actually what you need to do. Google this "CPU-Z" or "GPU-Z" (GPU-Z is better for GPUs) Although CCC does report that you haven't downclocked. When you look in CPU-Z or GPU-Z the clocks are actually just 300/150, or something along the lines of that. So in a sense it is running AMD Cool'n'Quiet.
It could be worth your while and it might not. If your proud to see your benchmarks be high then sure its great to OC. With my reference design card (it's different for everybody) I was able to hit 900/1200 without upping the voltage. But past 900 core clock you'd pretty much have to up voltage. (Though it's different for everybody.) BUT The downside to this, your temps will go up dramatically on reference cards or any for that matter.
CCC Is terrible when it comes to OCing. It seems like an OC really the OC is practically nothing in CCC, it's just like upping the core clock practically nothing.
Now, performance after OC. Before the OC in 3DMark Vantage, I'd get 14000ish. (Stock) After my 950/1200 OC I'd get 17000ish in 3DMark Vantage. All on performance. SO in a sense yes it's worth it. Games you play and resolution you play also may determine whether you should OC. On TF2 and CSS I don't need to OC, so OC or not there is like no FPS changes maybe a tiny different in different areas in TF2 but not in CSS.