Heatsinks help, but most of the VRM's cooling is on the motherboard ground plane, a direct metal-metal connection to the Tx core. Heatsinks get heat delivered on the outside of that nice carbonized silicon, through half-ash crap thermal tape. You might be reading 50+ °C on the top of that heatsink with an IR spot, but underneath, inside the Tx where it's directly grounded out in the core, it's quite a bit warmer.
Asus actually had the right idea, even if not so well thought out implementation. Active cooling the heatsink, not passively relying on blow past breeze from a cpu cooler. Keeping the vanes (not just a solid ish cover) cooler than the dissipation point means more heat is absorbed by the heatsink, less gets to travel to the ground plane, or if pushed to the same ground plane temp level, more power ability.
Gigabyte has done a great job, not only supplying decent heatsinks, but reinforcing the ground plane with thicker copper over a larger area.
You could take the heatsink from a good board, slap it on a budget board and it'd not really make much difference. The heatsink is just icing on the cake, it's the VRM's and what they are attached to that make up the cake itself.