In RL the Spit XVI was a late model Spit IX (e variant) with a Packard built RR Merlin. It had the bubble canopy and cut down fuselage also found on a few late model Mk IXs. The clipped wings were designed specifically for low altitude fighting. The Packard built Merlin was not constructed to metric specs and this was a critical difference with regards to maintenance in the field and ordering spare parts. For this reason it was given the designation Mk XVI instead of being classed as another Mk IX variant. It played a somewhat minor roll in late war combat as the Mk XIV was the air superiority fighter of choice at the time.
Most Mk XVIs had a razorback just like it does in AH. The real difference is that in reality most Mk XVIs (and IXs and XIVs at the time) were on 150 octane, and that means +25lbs boost for the Mk IX and XVI and +21lbs boost for the XIV instead of the +18lbs boost we have in AH. A Spitfire Mk XVI at +25lbs boost would need to be perked, no two ways about it. The Spitfire Mk XIV should have +21lbs boost in my opinion, as it is a perk plane.
