Pegasol 3440 Special and Solvent 3440 Special are the same and are used by some breathers I know.
Hydrocarbon, Liquid, N.O.S., is a generic name for hydrocarbons, but the one manufactured by Chemtrec is specific and very dangerous to use; so, don't.
As to how carcinogenic, that would be up-to debate since there is not that much research into either, at least in terms of cancer correlation in humans that I know of. An organic chemistry and biological explanation would be wasting both our time.
Instead, here are links to the MSDS for each.
http://www.mchem.co.nz/msds/Solvent%203440%20Special.pdf
http://www.inergypropane.com/midstream_wc/pdfs/Hydrocarbon.pdfAnd as always,
Fire Breathing is very dangerous. I'd stick to liquid paraffin. Is there a reason you want to use these?