Originally Posted by DieselDan
I'm using a 10-speed 105 rear derailleur with an 8-speed chain on a 7-speed cassette with no problems whatsoever. The derailleur doesn't care how much cable the shifter pulls with each upshift.
That is true for most Shimano derailleurs, but not true for pre-9-speed Dura-Ace which has a different cable pull ratio. Pull ratio is an issue if the shifters are indexed.
Al