A nice place to visit, Williams, out in the countryside and perfect for a test drive. They are a bit hard to find the first time you go there as they are set back from the road.
Ground (that is speed bump) clearance is generally not a problem with the 4/4 but the Plus 4 has the lowest tyres of the whole series. It really does depend on the tyre sizes fitted. I, and many others, have fitted 195/65 R15 tyres to gain an extra 10mm of ground clearance. 10mm doesn't seem like much but it makes quite a difference. A nice option is the Plus 4 with the narrower and taller tyres. Light steering and little more tendancy to oversteer, if you like that sort of thing and are prepared to drop back a couple of gears and give it some boot in the corners.
The 4/4 and the Plus 4 are really not so different in performance in the real world. The 4/4 requires a little more work on the gear changes but it has a wonderful revvy motor. The Plus 4 is a little more relaxed for touring but is a fraction heavier than the 4/4.
It all depends on your driving style and how you intend to use the car. All good fun