The enthusiast/gaming mobos are intended for very hardcore overclockers. They do have better components, stronger VRMs and more, but their benefits will only show up when you are doing extreme overclocking, probably with special water/LH cooling and gamers who also game with 4 cards or so. Average gamer playing with single screen and single or 2 cards will not really reach technical limits of mainstream boards. I think the Full ATX sized board, with 2x SIII, 2x USB 3 and 2x PCIe will be enough for any avid gamer today. The VRMs are strong enough and stable to work with 4.5 GHz overclock, but then again in name of gaming, the CPU overlocking does not bring much to the table anymore, it's the GPU performance that's important.
About the diagnostic display, my mobo does not even have 2 PCIe slots but it has the LED
The 80-100% OC was probably not even possible on Celeron 300 which is historically known best CPU to ever be overclocked, I don't remember how much the performance increase was back then but it was probably 40% performance increase.
Conroes OC'd well but you didn't get 80-100% increase, both in performance and frequency. If yes, than it's base overclock would be 5.4GHz(on air?) and performance wise it would be at the level of i3-2100, which was unreal at the time of their release.