You can absolutely long line and spider rig at .8 mph. It's really just slow longlining. And more so, side of boat spider rigging with extra weight. lol

Keeping the jigs in the zone (how far off the bottom) is really all you are trying to do. And also the right speed. Finding the zone and the speed is the trick. And you vary it all, with obviously your speed, but also how far out you let the line out and how heavy your jigs are. If you want more speed and lower depth, you have to let line out and or add more weight. Play with it. Pick you line up often and see if you're collecting muck. I've found here on Griffin I seem to have to be close to the bottom to catch'em. And I also know that if I got muck on the jig, there will not be fish on it too. You'll see me checking my lines and tossing them back out very often. Always gotta be doing something. Good luck, and your idea looks great. IMHO you could have placed a few closer together for more convenience, and changed their angle, or even perhaps use different rod lengths to get clearance from each other. I use all 6 footers off the back, and I use nine footers and 14 footers off the front to get the spread.