Just a couple thoughts, based on the standard calculation used, in order to get 6 knots you need at least 25 feet of waterline. Since length overall is usually longer than waterline you're probably looking at 27+/- feet to get that. There's only one trailerable I know of that's that long (the seaward 32rk), and it's way out of budget consideration. In the sizes you're talking about you get a boat with 4.5-5 knot abilities and you'll average 3.5 or so if you keep it lightly loaded. Pile on gear for a week, and you may not get that for an average. Remember the 5 knots is the theoretical hull speed. If your plan involves trips that require that speed to make them possible you might want to rethink. You won't get it from the boats you're talking about.
That said, a McGregor is probably not a bad choice, but you'll have a hunt to find one in your price range. If you can find one it adds the advantage of higher speeds under power so greatly increases your cruising range and the water ballast makes them really easy to tow.
I've sailed a Hunter 22 and liked it. It's simple, with a shallow draft, and might be a good choice for you. The accomodations are simple, but reasonable for one or two.
I wouldn't worry too much about a few feet of length. It won't make the difference in your ability to handle the boat, and in some ways a larger boat is a little easier to handle because it's more stable and you have more deck space to work on.
Anyway, good luck. I hope you find the right boat.