I compared a 4 foot octagon loop with my other antennas, never really used it as my main antenna, but it worked well http://n3ox.net/files/magloopnew_lg.jpg
It had a nice Jennings vacuum variable capacitor and it was able to tune from 60m up through 15m.
I feel like 1-2S units down is similar to what I've seen with my loop in real testing and in line with predicted losses for a good loop. The other drawback is constant retuning, but that wasn't a huge deal either.
It's kind of hard to beat a magnetic loop for being able to pick any band and set it up quickly and for being a totally self-contained antenna.
There are other compact antennas that can do a lot better. I built a 10 foot vertical for 40m that would work fine on 40/30/20 with coil tap switching: http://www.n3ox.net/projects/n3oxflex
I eventually implemented tap switching for 30/40 and it was my summer 30/40 antenna after I built it. I didn't really worry about taking it down. My alternate antenna for the lower bands was 60 feet tall and even with proper station grounding always stressed me out in summer Maryland thunderstorms.
It would be really easy to lay that over on a hinged base. Very lightweight. Would easily handle legal limit. And it had a combination of nice tuning range (which could be easily motorized) and a pretty wide SWR bandwidth even without retuning. Of course it needs radials, which can often be a deal breaker. But that antenna was only 1dB down from a full-sized 40m vertical.