JMJ,
They are good tractors. We have a 4430 powershift. Shifting issue is more than likely tied to cab mounts squatting due to age. This happens with every transmission option to some extent. I haven't heard of issues with the Quad Range and most people prefer them over the other two. I like the powershift myself but most don't like the jerkiness of the 8spd. Here are a couple of major differences of the 30 to 40 series comparisson. 1. Engine - 30 series has the 404 40 series the 466. The 466 is known to lug better at low rpms but both are good engines. The 4440 will have a few more ponies over the 4430 2. Rear End - There were failures in the 30 series rear ends that were corrected with the late model 30 series and all 40 series. Most(early and mid) by this time have been corrected but I would assume there are still some that loom untouched. Truth be told my guess is some of this was due to the ease of turning the juice up on the pump and running 20%+ over stock setting.
Also the 4430 production ceased in 77'. Might check to see serial number as the later serial numbers have a slight increase of value over the earlier ones. Not much maybe $500-$1000.
I wouldn't be afraid of the 30 series at all as they are good tractors but like most how they have been maintained is key. Knowing the person that owns it and has ran it is worth a lot to me. Only thing I would caution about the 4430/4440 is they are thirsty tractors so if your are going to use it as your main tractor it could be a waste of fuel unless you have big implements. Ours has been turned up and it will pull anything(21' disc/3yd dirt pan) we have but it won't pull past the pump.
Let us know what you decide.