I recently went from a Classic 3 with the 3D tonearm & dual pivot to a Classic Signature with the gimbal Fatboy and heard a significant difference with my Soundsmith Paua Mk II. It is significantly quieter in the grooves with less chatter. I had the HW 40 feet on the Classic 3 as well (plus it sits on a Symposium) and attribute most of the difference to the tonearm. I noticed improvement across the frequency band with low and mid-bass being the most noticeable change. Mid-bass is more three dimensional. Cymbals have more shimmer and there seems to be more space between the instruments/notes.
As I get older my hands get a little shaky sometimes which makes me nervous when playing records. Even if the gimbal Fatboy is not quite as good as the unipivot with the dual pivot I see myself enjoying the turntable more with the gimbal tonearm.
As others have said matching the cartridge to the arm is vital but you also need to consider matching the cartridge to your phono stage. The Paua and my Modwright PH9 X seem to be an exceptional match.
@Skyscraper will you install the Fatboy now and have the dealer assist when your Lyra comes in? Using the Fatboy with your current cartridge should really highlight the differences between tonearms.
I hope you'll enjoy your upgraded turntable!