https://docs.google.com/spreadsheets...9cBDAQ/pubhtml
In short, on a 100 regen tick test i healed less with +25 spellspeed than without the food bonus (sohm al tart), while i expected the difference between with and without buffs to be insignificant, i expected at least the average healed with food to be a tiny bit higher. Such thing was not verified.
I even recorded the ticks and ran through them a frame count, spellspeed did not affect the ticking speed either.
Edit : Assuming rng gods decided to bless me with max hits i decided to take a look at individual values rather than to the whole thing together (average). It seems 25 ss increased the most ticket HoT from 1117 to 1144 which makes a rough 1:1 scale. But the overall average makes spellspeed still a pretty bad stat lol.