I don't think it can be down to tired engines. We had quite a few 'Dogs at Old Sarum over the years and none felt happy cruising at 120kt - even when I put a new engine in G-BULL a 120kt cruise needed higher than the book power setting, 110-115 felt a lot more comfortable.
FWIW G-BHZT (ex-Botswana, I think) had far the nicest "feel" of any of the 'Dogs that I've flown - and even had hard points and a trigger on the grip
HFD