I actually haven't yet decided which way to go for definite. The car still has some stuff to remove before I can take any option at all, but so far, yes I'm leaning more towards the acid dipping.
Yes, I know there are some bad experiences, but there are also many very good ones. There are a tonne of bad reports about SPL, yet none relating to Pro-Strip (That I can find at least) and the E-Coat from SPL (Not done by them on site, done by another company elsewhere) is not the same as the zinc coating from Pro-Strip (Done by them, in the same facility as the dipping).
The acid dipping, I at least understand from a scientific point of view and can take various steps to try and prevent problems. For one thing, the acid dip at Pro-Strip, is not the same as the one at SPL and is completely non-corrosive to ferrous metal, unless it's in a state of oxidisation, so the neutraliser is purely for preventing paint reaction and not to stop it eating the metal itself. Again, this is unlike SPL, where they use a corrosive Acid, which needs to be neutralised to prevent it eating the healthy metal as well as the rusty stuff.
As for box sections, whether I blast and don't actually remove the rust inside the box sections properly, or I dip and remove the rust, I'm still going to have a problem with getting waxoil in there and I'd wager I'll probably have more of a problem doing that with blasting, where all I'm doing is covering up rust I can't remove with waxoil, than I will with dipping, where I'm going to be covering the bare metal with waxoil instead of covering rust.
Short version is, I still don't know, but yes, I'm leaning towards dipping with Pro-Strip.