I've always wondered and figured some of you may know. It seems these guys are often times very loud and strong all over. I've seen some of their photos online and many are clubs with nice beams at decent heights and such. But they're always loud and strong. Which makes me wonder what sort of power limits they have for HF. Anyone know?

@Gyprat

It's the antennas and them knowing how to take advantage of propagation. It's the reason they're the "big guns".

Quadrupling power only raises the received signal by 6 dB or one S-unit. The gain of the antennas is higher than that. On top of that, they're probably using stacked arrays.

Here are the rules for Slovenia.  Looks like 1500 max.

http://www.pisrs.si/Pis.web/pregledPredpisa?id=AKT_857

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.

That was what he was driving the finals with.
Back in the '50s and '60s, used 5 and 10 KW AM broadcast transmitters could occasionally be had for little more than the effort of hauling them away. Conversion to 160 or 75 Meters wasn't that much of a problem.

Most spend their money and efforts on antennas first. Maximum TX power varies by country and/or license class. Usually it's a kilowatt limit for the highest license class (Extra equivalent).
Do they always follow the limits? Heck no. Last club station I visited in Europe, was running an Acom 2000 amp. It put out about 2kW but they had stacked Yagis for 20, 15 and 10 meters. Of course it worked very well.
I've seen a club station using an old military amp. 5 Watts in, 10kW+ out. Official power limit on 80 meters was 5 watts back then, if I remember correctly. The amp did very well with a full size, 80m loop (at 150 ft). It was fed by a thick gauge ladder line, straight out of the amp.

One thing I did learn with putting up my Hustler is making sure it's done right and resonant makes a huge difference. That Hustler isn't even cream of the crop either. I was absolutely blown away at the difference. I don't mess with tuners unless I have to anymore. I'd rather take a week, or a month in my case, to have it done right.