Is the going long better for running shorter distances faster just because you are closer to target weight and fitter?
Fittest (and fastest) I have been is doing IM training. But then I have never averaged 12-hours training for 20-weeks before either.
Cycling is good for leg strength and this carries into running races.
My fastest 10k (OK only 48mins) I felt better at the finish than some previous PBs before I did IM. I could also have carried on albeit with a bit of slowing down whereas before I was done at the line. Didn't have the leg speed to go faster but did have the stamina endurance to use max leg speed for the whole race. So IM made me fitter, stronger, faster - well what a surprise of 20 weeks of solid training.
Shame I am not as well trained for IM this year.
M.eface