So the old suspension is out and I’ve replaced it a fresh set of springs and shocks from a MK6 GTI. I never realized how well the stock GTI handles. Seems to have more confidence in the corners. It also feels like it’s more fun to drive. Lowering springs may have affected the geometry enough to mar the steering feel.
The suspension pieces between both models are completely interchangeable. The valving and spring rates may be different, but as far as fit, they are identically.
(Available information suggests that the MK6 and MK5 cars share exactly the same springs and shocks, at least for the US market. The rear sway bar was supposed to be larger than the MK5 as well, but it may very well not be.)