I recently made the same upgrade you are thinking of. We had an old C22 and wanted more space for cruising and also something that felt more secure then the C22 swingkeel. Neither of us could ever get over the clunk noise everytime a big powerboat went by and got us with wake.
With a 6500 lbs tow vehicle you are definetely limited to the C25 at best and you will really be pushing it. The C27 can be trailered but not easily and not something you will do often. Trailers are available for it. If you really want to trailer you should limit yourself to the C25.
We decided on a C27 mainly because we couldn''t afford a C30 and I was only willing to consider a boat with diesel inboard. I want nothing to do with an Atomic 4. Both have inboards and real marine heads with holding tanks
instead of porta pottys.
The C30 is considerably more roomier then the C27 and is much more "seaworthy" although the C27 can take a lot. It hobbyhorses and has a less pleasant motion then the C30. It is also a little slower motoring. The only real reason that I would choose the 27 over 30 would mainly be for the financials of it. Either way you are into the size boat that you will be paying marina fees and winter storage depending on where you are.
Harrison Twp, MI