Just another thought--are you using a walking foot? When stitching in the ditch without one, I tend to "pull" my fabric thru the machine. I just let the walking foot do the work when stitching in the ditch.
I have an inexpensive Brother cs6000 and I LOVE to free motion quilt on it. I often have to remind myself to SLOW DOWN!! I found that I can set the speed w/the machine's control and it will not let me go too fast when I push on the pedal.
As far as machines, the previous post was right. Spend lots of time trying them out. I have a cheapie ( I LOVE IT) and a mid priced machine that I never use any more. I just bought a really expensive one but I plan on doing embroidery work for school/contract and I need the reliability and 20 year warranty. I'm sure you'll be able to find one that fits your needs.
Also, have you ever used the basting spray?? Saves oodles of time and beats all that hand basting--------wish I had used it years ago!
HTH,