I have a 'new-to-me', gently-used 770QEE that I bought in June and think it's an amazing sewing machine - I'm so glad that I bought it! If you're an active quilter, embroiderer, sewist (is that a word?) you will l.o.v.e. this machine and I think it's well worth $4,500.
This is my 1st Bernina and I've invested a fair amount of time watching videos and going through the manual as this machine is packed full of features that you must learn in order to enjoy using it. I also purchased the Big Book of Feet which has been very helpful, too! Next will be the Bernina Embroidery Book.
I've owned several other brands and am most pleased with the Bernina quality and performance.
Good luck in your decision!