bird photography on a budget

I am looking forward to buy my first 4/3 camera (still undecided between G3 or GH2 and DLSR). So far, I have been using a super zoom camera for the last 3 years (Pana fz28).

Looking at different prices on BH photo it does not seem that price should be the determining factor for my choice :

G3 (14/42 kit) : $579
GH2(14/42 kit) : $895
Canon T3i (18-55 kit) : $711

Not really a huge difference here.

However I am interested (wife says "obsessed") in birding, and therefore am interested in a long zoom lens

Lumix Vario 100-300 (4/5.6) : $499 (2.0 crop factor, equivalent to 35mm 600mm)
Canon 75-300 f/4-5.6 : $169 (1.6 crop factor, equivalent to 35 mm 120mm-480mm)
Canon EF 400mm f/5.6 $1,249 (equivalent to 640 mm)

In a perfect world I would be able to buy the T3i+Canon EF 400mm for a total of $1,960. I doubt this is going to happen anytime soon, though, so the G3+100-300mm might be my next best choice ($1078).

So my questions are :

• would the G-3+100-300mm be undoubtly better than T3i+75-300mm for my purpose (how would a cropped picture from the T3i compared with the same shot with G3)?

-any other alternative for a $1000-1400 budget?

sorry if my question seems terribly naive to some of you, btw.