I replaced the stock crap cooler with this model:
COOLERMASTER GeminII S524 Version 2
It was not easy
Steps:
1. remove stock cooler and remove motherboard from case. By removing the GPU, and a few cables like the cpu power cable, and case fan, you can remove all the mounting screws and then lift it at an angle, revealing the metal cpu socket backplate that is on the boring side of the motherboard.
2. Discover that the backplate is how the cpu clamp - that little tray with the lever, that nails the cpu down - is attached to the motherboard. If you remove the backplate, which is just removing those three screws, the clamp is detached. That isn't what you want to see because aftermarket coolers have their own back plate design and don't have threads for cpu clamp.
3. Therefore, you need to keep the original motherboard back plate...
4. This aftermarket coolermaster has four spring loaded mounting bolts that you cannot turn (or even get at with the cooler installed), they are designed to be bolted, from the other side of the motherboard, via the backplate..
5. Drill out the four screw threads within the stock backplate, and file/dremel down the associated four sleeves, the ones that fit through the PCB. This allows the coolermaster mounting bolts to be pushed through the pcb and appear with enough thread on the reverse side. Now you need to obtain four little nuts to screw onto them because the ones in the kit are so large they cannot be turned, due to the HP backplate design. I had four little nylock nuts that worked.
6. Mount the cooler in the one orientation that works: looming over the memory boards.. There is only a tiny bit of clearance to the GPU also. You may want to stick some insulating material between the metal edge of the cooler and the GPU board, in case the PC is dropped while on, and they short.
7. Re-assemble everything , remembering attach the CPU power cord into the motherboard otherwise you get no beep, no POST and freak out.
8. The black GPU bracket HP give that holds the corner of the GPU, is not strictly necessary, and that's good because it can't be fitted now, without cutting a bit of metal on it..
Note with this orientation, adding memory boards is basically impossible, without removing the motherboard again and detaching the cooler. You should also attach the cpu fan connector before mounting the motherboard otherwise there is no space to get your fingers there.
RESULTS.
before: with prime 95 cpu heat stress test: 90c on each core, I didn't want to run it for more than a few minutes.
after: running prime 95, temp tops out at 71c