For your HK I recommend Aguila's. I carry them myself in my 220. They may or may not develop 700 ft lbs of energy, but they will very likely stop whatever is likely to attack you.
I just checked Aguila's website and the only two loads they list is a 230gn FMJ at 751fps and 352ftlbs, and a 117gn alloy HP at 1450fps and 546ftlbs. Not quite 700ftlbs (or 750ftlbs if you're using some of Double Tap's full-power loads). I think the .45 is an outstanding cartridge and I feel totally comfortable carrying it around town, but when walking out in the woods I prefer something with a bit more punch. Sure I could pack my .44 Ruger SBH or S&W M57 .41 Mag, but I prefer semiautos.
The 10mm can be loaded to 700 ft lbs of energy. BFD. Why is 700 any better than 600? What will the cartridge do that cant be done by what exists already? Nothing.
If 700ftlbs is no better than 600ftlbs does that also mean that 600ftlbs is no better than 500ftlbs? At what point do you stop? I do believe that there is a point at where more velocity, energy and penetration add nothing to the terminal effect, but that point changes when you change targets. As I stated I think the .45 is a very effective cartridge. That effectiveness is dependent on two factors though; target size and target distance. When shooting at a man-sized target at normal combat handgun ranges I don't think the 10mm will do much better. When you extend the range though the 10mm is a flatter shooting cartridge and that added velocity and energy means deep penetration even at longer distances. If you change the variables in the other direction and now have a much larger target you don't need a flat shooting cartridge, but you do need deep, deep penetration. The simple truth is that the 10mm can do anything the .45 ACP can do, but the .45 ACP
CANNOT do everything the 10mm can.
The term "better" means different things to different people. To some "better" means that the particular cartridge is inexpensive, readily available in any location and chambered in a multitude of different makes and models of firearms. To others (myself included) the word "better" means one particular cartridge provides greater ballistic performance than another. Considering that the 10mm is available in a greater range of bullet weights, can be pushed to far greater velocity and energy levels and can be had in the same sized firearm platforms I believe, without reservation, that it is a "better" cartridge than the .45 ACP. Does this mean that the .45 ACP is a lousy and worthless catridge? Not at all. You also mentioned that the .44 Mag is more powerful. This is certainly true, but none of your "magnum" revolver cartridges can be chambered in a semiauto the size of a standard 1911 (or smaller if you go down to the Glock 29, Witness Compact, etc.). Additionally, in most magnum caliber revolvers you are limited to 6 or so rounds. Take your Glock 20 and you've got 15+1 rounds (or 17+1 if you use the extended base pads) on tap. 16 rounds at 700ftlbs each is a lot of power in a standards sized handgun no matter which way you cut it.
So, to answer your question, yes the 10mm Auto can do things other handgun cartridges cannot. It gives you better ballistic performance potential than any other common semiauto caliber and yet still fits in the same handgun platform envelope.