Check out the section on sway bars. there is a link that can take you to a web site that has a lot of data on sway bars, hollow vs solid from Whiteline.
The issue of solid vs hollow tubes is seriously addressed on this article. Weeding thru all the calculations, you will find the hollow tube is approx 15% less strength that solid, plus there is an issue the irregular bends and the strength vairations of the bars due to this. this issue is not present in solid bars, which is the reason Pedders uses solid bars.