Found the answer, not documented anywhere but from a Netapp guru friend.
SHELF performance: YES, it will degrade the FiberChannel LOOP connectivity to 2gb, disallowing it the 4g/8g connection found in dsmk4/esh4 shelves. It will NOT degrade the IOPS performance of the 15k disks on the shelf, if they are within a different aggregate.
RAID GROUP: Yes, it will degrade the IOPS performance of the Aggregate as a whole if there are 10k rpm disks in the Raid Group
FC LOOP: It will not degrade the performance of the loop to 2gb connectivity, disallowing it the 4g/8g connection found in dsmk4/esh4 shelves. Guru's actual words "It will make it to where the loop speed can only be 2G instead of 4G multipath. The only way to achieve a 4Gb/8Gb multipath is with a DS14MK4 shelf, ESH4 modules and 15K disks…otherwise it is a 2Gb/4Gb multipath loop."