As a former '95 non-Federal VX owner and current '95 DX w/ VX tranny owner, here's my 2 cents.
I used to average 55 mpg during the summer w/ my VX for my 150 mile round trip, 90% highway commute. Little to no coasting, 65 - 75 mph, tires to maximum sidewall pressure.
With my current DX w/ VX tranny, I'm averaging 57 mpg the past 90 days, but I work my a$$ off for that FE. I do lots of hypermiling: drive 50 - 55 mph on the highway, engine on and engine off coasting almost every opportunity, tires at 51 psi (sidewall max for my Sumitomo HTR T4).
I think if I had hypermiled my VX as I do my DX, I would easily get in the mid-60s. That said, I think you're doing pretty good at 50 mpg w/ a 35 mpg car, and I'm not sure you would get the same jump if you were driving a VX the same way you drive your DX.