Hi, Avanti1960, I've been using an ART9 with my SME 309 (9.5g effective mass) without problems and it sounds very good, even surpassing a Dynavector Karat 17D3. The one potential problem using the ART9 (or ART7) with a lighter weight tonearm is subwoofer pumping, as discussed here: http://db.audioasylum.com/mhtml/m.html?forum=vinyl&n=1141823&highlight=art9+pumping&sear....
I use sealed subwoofers so haven't had that problem. People with ported or servo subwoofers can use a rumble filter.
Regards,
Tom