I currently have a 40m loop fed with ladder line all of the way to the shack (probably closer to 45 to 50m in resonance). The loop is 5 floors up. It gets out for DX, but not as well as a resonant flat-topped dipole positioned well, and at same height. I'm going to say about 3 to 5db difference on 5,000+ mile DX. I'm coming to that conclusion based on listening to my own TX signal from here in Korea, using websdr.org's station based out of California. On anything below 3,000 miles, it's pretty outstanding on 40m. It's best for contacts 1,000 miles and under -- omni-directional TX and RX, and a bit more quiet receive compared to a dipole -- varies between same to 1S noise difference, but it really depends on the noise, and where the dipole is favoring (I am in the city). If you want omnidirectional coverage of North America, the resonant 40m loop is great on 40m. Same said for an 80m loop on 80m. An 80m loop is said to work great on 40m, with some gain lobes and weaker null areas. If you get into higher bands, you start finding lobes and nulls will affect where you can work. Different heights and frequency will affect where the non-resonant band lobes are, and at what angle. Loops aren't something you easily rotate or move, obviously. With a dipole, you may be able to move it around more easily to work those other areas when you want to (just move the legs). After several experiments, I find the large sky loop is great on its resonant frequency, but hit-and-miss compared to a dipole on higher frequencies. They are very convenient in terms of just having something that you can always tune to most any band you want, if you have low-loss ladder line. Having 1 antenna that works decent enough across multiple bands is very nice to have. Having a loop, plus a smaller rotatable dipole for the high bands is even better. I've learned that resonant monoband dipole's at good height work best. A double-extended zepp with ladder line feed is also great, and is more easily adjusted for lobes/nulls than a loop. The loops advantage is it's farily quiet (as a horizontal), omni on its resonant frequency, and a really great rag chew antenna at sub-1,000 mile distances. A look at mine: If you have a few trees around, and want to put up a nice antenna that will generally perform very well -- by all means, put up a sky loop! They're fun.