@happyjet there are a bunch of videos on YouTube about that fiddle.  From what I can gather,   they are excellent violins. Certainly Scott Cao is well known and respected in the  business, so you know for sure it's not junk.  The 750 series is their mid-priced violin and the backs are made from Chinese maple, whereas the more expensive 850 series uses european maple.  How much difference does that make?  I have no idea, but I doubt that you or I could tell the difference. I don't know about you, but if I see nice flames, then I think it's good maple (even though I may thump the wood to test for tone, I do so at about the same level of expertise as someone who kicks tires to judge the quality of a car). I think the same business model holds true for the GCV and MJZ violins as well.

The formula, for the math inclined is: more desirable wood + more experienced luthiers = way more dollars.  

The 750 signature series also has copies of at least a dozen different famous fiddles, both Strad and Guarneri. If you decide that's the direction to go, you will have even more deciding to do. "Hmmm, do I want the Soil copy, the King Joseph or the Vieuxtemps.   Oh, wait, maybe I'll get the Kreisler..."   Good luck with that decision.   

Whichever way you decide to go, Scott Cao, Scott Cao famous fiddle copy, FM GCV soloist, FM GCV famous fiddle copy, MJZ, you're going to end up with a good sounding instrument that sounds great, looks good, is easy to play and will serve you well for many many years.  Have fun deciding and I can't wait to hear whatever you get.