Agree: some of these folks have really tremendous towers and antennas. It's not all Eastern Europe, either. Who here has not had a QSO with Dave, G0EVY, on either 80M or 40M?
His full size 80M beam using a 150ft high mobile crane for a tower is pretty amazing.
AFAIK, the largest, easily available (but pricey) solutions top out at about 5KW. Most notably those would be the amplifier combiner systems from Acom (3 x 2KW - losses) and, IIRC, there is an Aussie firm selling a combiner for dual SPE amp's. At this power level you start to run into problems with obtaining baluns and commercial antennas that will handle the power.
There are, however, plenty of US hams that run extra-legal power. There used to be a lot more when AM was a bigger thing. I personally know a relatively local ham that built, and uses, a 7KW tube amp. He shunt feeds a tower on both 80 and 160M. His signal is truly awesome. When you ask him how much power he is running he will always respond "700 Watts"
A business colleague of mine used to work commo for Dept. of State back when HF mattered. He always told me that there was very little you couldn't do with 10KW and a 80-10M log periodic at 100ft.