The r/t sways aren't all that aggressive. Put them on, I think you'll be happy. Hotchkis makes fromt/rear sways that are even stiffer than the stock r/t sways

The 'equation' for a hollow bar is to pretend you're dealing with 2 seperate solid sways. If you have a 7/8" tube with 1/8" thickness, then the diameter of the open space is 5/8"

You would calculate the strength of a solid 7/8" bar, then subtract the strength of a 5/8" solid bar

Sounds like a lot, but as mentioned, there's a torque involved with sways, so the farther out from the center, the more work the tube does. You can use a larger hollow bar to increase the spring rate of the sway bar, without adding additional weight