any entry level low profile graphics card will do for 660s.  If your 3010 is DT or SFF, yes too.  If 3010 MT, needs a full height simple video card.  HD6450 is fine, it is an old simple card c/w old dell such as 660s or 3010.  If one of your monitor has hdmi you can also skip the card and just use onboard video ports of 3010 or 660s  VGA+HDMI to run two monitors.  It supports multi display. [IMAGE]  
I'm looking for a non-gaming dual monitor setup wtih a discrete card because I'm looking at installing a Xeon in there which does not have integrated graphics. (thanks I think it was Fireberd who mentioned UserBenchmark as a resource) Actually I could use my other machine (Optiplex 3010) for that so really ANY low powered card that's low cost will do, and I've been looking at the HD 6450. Would there be any concern with putting this with the original PSU on either machine? I have only one stick of ram, SSD and would disconnected the optical drive if needed. I believe the 660s is 220 watt and Optiplex is 240? Really just want to have one screen as speaker view on Zoom while the other is on gallery, though if needed I'd just do that with the other machine with a i5 3450.
Inspiron 660s discrete graphics suggestion