Two years ago I bought a Juki TL 2010 Q for machine quilting and I love it. This year I bought a new Bernina 770 QE and love that one too. It has the BSR and I'm finding it helpful.
I noticed something though: while the Juki has a nice harp space (as does the Bernina), the Juki is taller because there aren't any electronics ( screen etc) that the Bernina has. But let me tell you the new Bernina is amazing!!!!!! I've been sewing with a Bernina 150 for almost 20 years and the new one is a fabulous machine.
I haven't had tension problems with the Juki but I can't get the threader to work. The Bernina threader works great.
Had I known I was going to get a new Bernina I'd probably not have bought the Juki but I love it and now I can sew on one and quilt on the other without changing anything. The Juki is very affordable.
So in my opinion, yes, a larger harp helps a lot. My skills are improving much more than when I was trying with my older Bernina.