I would have bought the 28 over the 270, the admiral likes to bake, and fresh muffins is reason enough for a 28! The obvious drawbacks, the 28's that we found did not have trailers, and that's a logistical nightmare from 500 miles away (or however far) and even with a 3/4 ton diesel, the extra 2000 lbs is a stretch, not to mention that the 270 is BARELY legal, and the 28 is a lot wider (highway wise), so for us, the 270 was the choice.
I have a 135 and I know that the 155 will fit on the cabintop tracks. I added the winches at the back, and am working on a couple of spacer blocks to raise the lines above the cabintop so it doesn't wear the gel at the back of the track. In fact, a slightly longer foot (by a couple of inches) than a spec 155 will fit just fine on the cabin top. (There's a nice roll of laminate at FX waiting for a phone call after the mast is up and the tape measure comes out)
The difference in performance between the 135 and the 155 is not insignificant. I know of a few folks who have a 155, and they would never go back. I got a drifter from National for light downwind and it flies just fine wing and wing.
I'd really like to have an honest drag race with a 28 (wing) to see the difference. I know the 270 accelerates better, but a well understood 28 could use the extra weight to a huge momentum advantage in a forced ownership campaign on the course.
Cheers
Gary