3.Will either of the two cameras match up to the performance of a 650D?
to match Sigma 17-50 f2.8 and Sigma 30 f1.4, don think there is a equivalent of M.Zukio 8.5-25mm f1.4 and 15mm f0.7 but there is M.Zuiko 12-40mm f2.8 and 17mm f1.8[/url]
You're comparing APS-C, not FF, with m43. Divide by 1.25, not 2.
The 12-40 (m43) IS roughly equivalent to the 17-50 (APS-C)
For the 30mm (APS-C), the equivalent is 25mm, and there are some great m43 primes - Pana Leica 25/1.4 or the less expensive Oly 25/1.8.
As for aperture, f1.4 is f1.4, no matter the format. The light gathering power is the same, ie. all other things being equal, they give you the same exposure.
The DOF is greater for m43, so if you want to blur backgrounds with selective focus, you need abt 1 stop bigger aperture for m43 than APS-C (2 stops compared to FF). There is a Voigtlander 25/0.95, but it ain't cheap. If that's important to you, you might want to go up to FF instead. But if size and weight is impt, m43 is fantastic.
The 650D is a good entry-level camera. The EM5 is more like the 7D - semi-pro, tougher, and with better direct control (2 dials and lots of customisable buttons). So performance-wise, you'll probably find the Oly's faster in almost all situations. That goes for the EM10 too.
Image Quality? Not much in it, even at high ISOs. Since the EM5 (1st one), m43 is abt on par with APS-C. That said, the image processing engines are different, so if you're shooting JPEGs, there is a different look. Subjective. I am happy with both, but prefer the Oly.
You might find the Oly menu system a bit convoluted (I do, buy maybe I'm just getting used to it. I'm more used to Canon's too). But compared to the 650D, the Oly's offer more customisability. After all, the 7D menu is also more complex than the one on the 650D.
All in all, I think you'll be very happy with the move. Just bear in mind that no system is perfect. You will probably need some time to learn the ins & outs, and make the most of it.