Another thing not mentioned about having the riggers so far out is stress on the gunnels. A 30 inch boom with a 15lb weight will give you about 45 foot-pounds of torque, plus a bit for water resistance, at 60", you'll be putting on 90 foot-pounds of torque on the gunnel. That's like having someone stand on the boom 6" from the downrigger at all times. Now imagine someone jumping on that boom while you brake it going down. If you get snagged with fresh, unafraid braid/wire, you'll be putting up to 750+ foot pounds of torque on the gunnel before it ends up breaking the line if your brake seizes. In a little aluminum boat that is enough to completely f#$@ it up. Not to mention that from the whole boat's perspective, that's the same as putting 2 170 pound guys on one gunnel, I wouldn't risk it. I've got extendable scotties, but they're always fully retracted. On my previous boat, I used a 12" wide 1 1/2" sheet of marine plywood to eliminate that torque, but still kept em in nice and close.
Turn slow, keep the deep side inside, so the higher side rises up, use slightly different weights(10&12, 12&15) putting the heavier on the deeper side, and you shouldn't have any problems in the turns. I find usually 15' back is enough so you don't see the flasher movement in the rod tip.