Replacing my RX 470 cooler with a R9 280x cooler?

[Crestfallen_12]

So I have a Rx470 from powercolor single fan, and I replaced the bracket as you can see here:

While it's better now, it still throttles at games even at 100% fan speed. I do have a Msi R9 280x Twin Frozr heatsink, but it doesn't fit because of that metal part on the VGA cable connector on the GPU. Would cutting out a piece of the heatsink fix the problem, and give me better cooling?

I don't want to spend too much on watercooling or aftermarket coolers.

 

[yeti_yeti]

I think replacing the thermal compound and cleaning the card off dust would be a much more efficient solution.

 

[Crestfallen_12]

The card is clean, this picture was taken through the side window and the fans are running(looks like dust on the pic). I also replaced thermal paste a few months ago(artic silver).