AIUI putting a more powerful engine into the Hurricane didn't make the Hurricane Mk II much faster than the Mk I, but IIRC it was heavier as well. Again, AIUI plans to put the Griffon in to the Hurricane were abandoned because it wouldn't make the aircraft that much faster.
Hurricane II was also draggier than MkI, due to having BP windscreen, nore guns, and later cannons. Added drag eats speed far easier than added power can add speed.
Hurricane, in general, was an high-school exercise in how to make a fighter go slow.
I suspect that that the same would have applied to the Henley and for that matter the Hawker Hotspur.
I haven't checked but IIRC putting more powerful engines into the Fulmar didn't make it significantly faster. However, I have also been arguing for years that the main problem with the Fairey Battle was that it was underpowered and that had it been given an engine in the Griffon class (which AIUI was the plan, but the engine was cancelled forcing the Merlin to be substituted) it would have been a half-decent aircraft by 1939-40 standards. I've also suggested a Twin Battle with two Merlins, which I think would have been a worthwhile improvement over the Blenheim Mk IV in 1940-40 in the light bomber role and also as a night fighter in the Blitz.
So I may be wrong.
Hawker Hotspur was a college-grade excercise in making a fighter go slow - take a thick wing from you current draggy fighter, make it even bigger for more lift (and drag) so it can carry bombs, mate it to a big fuselage (= extra drag), then add turret to make it even draggier. Duh.
Henley at least didn't featured the turret, so adding the Merlin XX or 45 should cancel out the speed lost due to added guns and navalization.
As noted in other thread, new engines for Fulmar were still of the low-level flavor - not much of speed they will add.