Agree with Ed
The toerail is a very strong attachment point, and it is backed up by the hull to deck joint, also very strong. If your backstays are like mine, they are attached to u-bolts that are backed by large washers, under the hull-deck joint, under the toerail. And the loads on the rig are way higher than for a spring line. Using the toerail also eliminates the chance of compromising the balsa core in the deck, through water penetration, crushing or whatever.Of course, if you need to move dock lines around, you can also just run the lines through substantial snatch blocks, and set them exactly where you want them. In storms, I usually run some lines from the winches exactly this way, but I like the idea of the permanent ones on the toerail. On the other hand, I adjust my jib sheet blocks over a range of about fifteen holes in the rail, so I will have to think carefully about location.