Crockusbird: The SME manual detailing the differences is at:
http://www.analogue-classics.com/html/sme_3009___3012.html
This is an excellent site with a handy tonearm-cartridge matching graph. Have fun with your Series III. I went out and listened to "modern" turntable/arm/cartridge systems costing up to $10K and was not especially impressed. I suspect that a good high-compliance cartridge, properly loaded and set up, will sound great with your arm. I spent about 40 hours optimizing my turntable/tonearm setup and plan to spend more optimizing the loading with my Shure Ultra 500. Also you will have less record wear than the current heavy-tonearm, high tracking force, medium compliance systems. I think it is time well spent. Regards, HG