I have a Bernina 430. It has a few inches more than the machine you have, and also is taller in the throat, but is not exceptionally large compared to some machines.
I can get an entire twin size quilt into it- with only a small amount of effort - to quilt all the way on the far side (I quilt better pushing away than pulling towards me, so I prefer not to have to go from the middle and do one side upside down.) Quilting from the middle of a twin is no problem at all, I imagine a queen won't be either. I don't think there is anyway I can get an entire queen in there though. I think a king will be doable, but hard.
It is by no means a budget machine, but it was $1000 less than the other machine I was looking at (Janome 7700). I prefered the Bernina's sewing to the Janome's, though the space of the Janome was to die for (to get that kind of space in a Bernina it is BIG BIG BIG bucks). I also think the Janome has much better memory capacity than my machine. My machine does embroidery, and the dealer threw that in free, but I'm not sure what I'll use it for. Still, it is nice to have an additional feature. The Janome was sewing only. Bernina accessories are expensive, but I found the ones I wanted for Janome were too- the Janome comes with a lot more feet though, so you won't need to buy as many. The Bernina comes with a darning/FMQ foot, but I bought an open toed one, as that is my preference. The walking foot for this machine is $$$.
I was using a sewing machine similar to the one you have, and found that it wasn't worth upgrading if I didn't spend at least $2000. The machines in the $800-1200 range just didn't offer enough to bother, I might as well just have stuck with what I had, instead I decided to make the jump to an expensive machine.
Also- while I had done some practice FMQ on my mass market machine (Kenmore 16221), I had lots of tension problems, and eyelashes, but not bad for a beginner. These all instantly fixed themselves on my Bernina. Now my only problem is keeping the stitch length consistent. Of course, if you get the 440 it comes with the Bernina Stitch Regulator, which was amazing to play with, but too much money for me. (It also doesn't draw the lines for you, and really, more than anything, it is the drawing that I have problems with. My whiteboard gets a lot of practice before I take a design to the quilt.)