For $620,-- it is probably the best deal you can get. Only if your budget goes up to a little over $1000,-- you can find some competition from other brands.
I did the same research back in december but decided to go with a Roland G1000. Got it from George Kay, who gave me a great deal.
In my opinion the yamaha 640 and 740 do not even come close to the G1000.
But I almost bought one of the yamaha's too until I realized that I could get the G1000 within my budget.