Around 4.5GHz is certainly reachable, it just takes a lot more voltage to be stable and the resulting heat rises faster than ever. The Ivy Bridge generation is like that. Doesn't feel worthwhile to me but one can always experiment.
The Z77A-G43 has two 4-pin fan headers near the front which should come in handy. Should be able to regulate both PWM and voltage, though I have really only used 3-pin fans on my G45's "system fan" headers. The controls are of the "set a temperature target and forget" kind of thing, but that can be enough. Personally I'd settle for having the front fans at a low steady speed and fiddle with regulating the others. I'm using the CPU fan header for my exhaust, since that's the only PWM fan in the system. With motherboards in this range the CPU fan header tends to be the best regulated one. And it seems so since it's able to take this TY-140 fan with a nominal floor of 900 RPM down to 700 RPM as long as the CPU temp stays below the set target. That's an improvement that came with some version of the BIOS by the way, as it used to sit at 900 RPM when the board was new. So another reason to keep the BIOS up to date.