I don't _really_ know the answer to your question.
(but I could be completely wrong) is that mixing binaries (that are expected to work "together") built using these different GCC versions may not work in the same way as they supposed to work. I mean, probably if _all_ is built with GCC 4.7.1, then it should work correctly (?). OTOH, maybe there won't be any problems, and the "incompatibility" may only mean that the building won't be exactly "reproducible" (?).
My concern is that, according to the GCC changelog, 4.7.2 is not just fixing some bugs in 4.7.0 and 4.7.1. My concern is that 4.7.1 (included in Slackware 14.0) is stated to be "incompatible" (well, at least regarding a specific matter).
You and The Salix Team are undoubtedly more knowledgeable to understand and evaluate the consequences. Maybe Pat would like to release some update in the near future (?), but I think fellow capable developers should evaluate this (as oppose to a simple mortal user as myself) and eventually suggest this update to him, if relevant.
Sorry I can't be of real help