If what I have seen so far is correct (such as this 'Tec and your Schomburg signed MMC book) 7.5 seems to be the cut off for a non authenticated, cover signed book. Both this book and yours (Rich) seem to be nicer than 7.5 and simply limited to the grade because of the hand writing.
R.
They do both look nice, but I don't know if they comprise a large enough sample to make a definitive statement on how CGC views signed books.
What would you have graded your Schomburg signed MMC book minus the sig...
BTW, got a scan of that sweet li'l thang' hangin' around?