Wait for the Mk7 personally.
You are right about the differences.I drove the mk6 a few times, and it has a nicer interia tbh and thats abit it. XDS is good aswell.Slighter better mpg by a couple of mpg.
Mk6 is more refined,less wind noise intrusion into the cabin... but on the downside, it has less in driver feel feedback
Rattles are normally loose screws behind the dashboard on the mk5, easy fix and not a finacial reason to sell up.
Mine is nearly 4 years old, and not a single rattle after 50k.
Mk7 should hopefully be a clean slate. And worth trading for, but thats just my oppinion from driving both.