Adding a Bequiet Slim 2:
As per other online suggestions, it's possible to replace the stock heatsink. Not absolutely necessary since the temps I showed above aren't absolutely horrible, but certainly can't hurt. That said... there's a height limitation so we're stuck using either LP downdraft coolers or tower coolers w/ 92mm fans. The one I've seen mentioned most often as an "almost" drop-in replacement was the CM Hyper T2, but I'd also been eying the original Bequiet Slim so it was pretty much destined to be when I saw reviews coming out for ver 2.
The only thing to keep in mind when sourcing a cooler for this is that you can't install an aftermarket backplate without major modifications (the existing one is part of the case side? ) so it needs to be a cooler that has mounting similar to what you'd see on a WC block with the appropriate arms with holes that will accept an M3 screw.
On the left in the second image is what you're looking for in mounting hardware.... basically arms that attach to the heatsink with holes that line up with the standard intel 15XX spacing. We're not going to use the existing plastic mounting method and they're easy enough to remove by rotating them to the flat spot and then prying up a bit on the tab I've indicated in the last image.
I don't have any close up images of it, but once that's done, and the stock dell cooler is removed all you need is 4 M3X16 screws with washers that are large enough to secure the holes on the cooler's arms and you're good to go. (They'll thread right into the existing backplate on the board). I went a step further (just because I had the hardware on hand) and used some spacers between the bottom of the arms and the motherboard (The spacers measured @ 3.85mm, but I would have gone a little shorter if I was going to print them off), but that's not absolutely required, just make sure you're not torqueing the screws to a point where you're going to bend the arms.
There it is installed with the case side on and off.... The "button" tips for the tube ends is a nice touch, and makes this $50 (to the door from B&H) cooler look a lot less budget than it actually is.
Stock Cooler at "performance" settings in the alienware control software.
And there you have it.... 12C improvement at full load using the stock "performance" settings in the alienware control software.