I think it was undergraded personally and could possibly go 7 or even 7.5 if cross graded by PSA
1956 Mickey Mantle Possibly Undergraded as A 6 80 by SGC Possible PSA 7 7 5 | eBay
And more mantles (raw)...
http://www.ebay.com/ulk/itm/322003598521
http://www.ebay.com/ulk/itm/322005191857
http://www.ebay.com/ulk/itm/322005193623
http://www.ebay.com/ulk/itm/322005194367
1956 Mickey Mantle Possibly Undergraded as A 6 80 by SGC Possible PSA 7 7 5 | eBay
And more mantles (raw)...
http://www.ebay.com/ulk/itm/322003598521
http://www.ebay.com/ulk/itm/322005191857
http://www.ebay.com/ulk/itm/322005193623
http://www.ebay.com/ulk/itm/322005194367