Hmm, just read the other replies about handling.
I personally felt coming from a 99 2.0L TS that the handling is better in the GT in terms of corner grip.
The 156 was lot more nimble though, but then it was 0-60 in 8.2seconds I think, and the JTD GT is ... well its more 8.6, 9s I forget, but with all the torque it does not feel slow. You adapt as well, rather than rev high you use the low end shovel instead.
shiny car - all the V6's are front heavy, its a V6 thing not a GT thing I think, the GTA I drove and 156 2.5V6 felt the same.
I think the rattles are subjective as well, I have one at the back at the moment as its so cold and the rubber on the rear shelf is all hard. Its not annoying though, and not really noticable with the stereo on, and I am sure I could fix it with a dab of silicon grease or foam or something if I felt the need.
The only real downer from a 156 is that there is no rear door for your granny, so she has to sit in the front and you have to get the wife to clamber in the back.
Also, you can get permanent rear passengers. Its easier to get in than get out, so those of considerable frame may find themselves able to climb in but struggling to get out!