Well I finally got the W5GI "mystery antenna" up at around 55-60 feet, strung between a tree on one end and a mast on top of my house on the other end. It is approx 103 feet long, and is center fed. I am feeding it with RG-8 coax.
It has <1.9 to 1 SWR on 80, 40, and 20 meters. It is a little higher than 3:1 on the higher bands, but my vertical works well for 17, 15, 12, and 10 meters. The W5GI is working GREAT on 20, 40 and 80. It is a resonant 3 element collinear array at 20 meters, and 100 watts have so far netted me Spain, Italy, Slovenia, Argentina, USVI, BVI, Mexico, Trinidad, and Barbados, as well as several US states and Canadien provinces. And that's with really casual approach, only a few hours tops over the last week or so. I can seemingly get back to anybody I can hear on 40 and 80, and get lots of 59s on those bands as well.
I have it oriented to favor 40/220 degree paths, but it seems to work fine in all directions.
The materials worked out to about 40 dollars per antenna. The most expensive component is the 300 ohm ladderline, which everybody was out of except the wireman.com, and they only had the more expensive .27 per foot stuff in stock.
I am very pleased with the antenna, and highly recommend it. It works really well. When we had it temp mounted at only 25 feet it was a little anemic, but it came alive when it got up above 50 feet.
I am going to build an off center fed dipole that Sonwatcher sent me a link for, and try to set it up to favor a pattern perpendicular to that of the W5GI, and be able to switch between the two.
Then I want to try to make a 2 element 6 meter Quad. I got an old RatShack rotor for free, and it works---should be plenty to turn a small quad.