I bought this mobo: Asrock H81M-HDS. Reviews seem to be good, but here and there people claim that when you put a big GPU(like the R9 280X) into its single PCI-E slot, it will block access to the front panel connectors. Could somebody with this particular model maybe tell me if this is the case or not?
Gee. That's an m-ATX motherboard with only two PCI-E slots. I had looked at your thread and question briefly, and thought I'd leave it up to someone else.
I finally took a look at the picture-gallery at Newegg for that board. At first, the idea of the front-panel pins being "blocked" seemed absurd to me. Then I thought about "a big GPU." I can't imagine even a "big GPU" overhanging three-PCI-slots-worth of space; I would think it would only cover one slot -- taking up a total of two PCI slots including its x16 PCI-E.
The AsRock board's second slot (possibly an x1 or x2 slot) seems to be removed from the x16 slot by approximately two PCI-slots-worth. That is, they could probably have fitted a second PCI_E or PCI slot between the two.
The front-panel pins seem to be "right on the edge." A big GPU might just barely overhang a couple pin positions of the front-panel pin-out strip. But those holes in the strip are vacant. The remainder of the pins likely would be visible with the beefy GPU installed.
I suggest that you can plug in your front-panel LEDs and switches with the GPU installed. if there were a problem, it wouldn't pre-empt you from using the motherboard. It would merely be an inconvenience. You'd have to remove the graphics card to reach the front-panel plugs to remove or install them. That being said, once your system is built, up and running, you wouldn't often find the need to access the plugs and pins.
But -- I still think you're "good to go." It's "close," but that only counts in horseshoes, as they say . . .