And you will find it goes just that little bit slower and used just that little bit more fuel than your troy-built.
If you want to compare gear boxed to hydro to variable belts then you have to do it with what is in the showroom today not what was sold 30 years ago.
The landlord has a host of farm tractors from the 40's 50's & 60's ranging from 20Hp to 45Hp and these pull hoes, ploughs, dig holes and lift 2 ton, SLOWLY.
Two models sitting side by side, the vari drive one will generally have a smaller engine ( next year it will get bigger and continue doing so till replaced with a new model ) .
The manual PTO will have a smaller engine than the electric PTO.
Both Briggs & Kohler recommend the mower companies work out the power requirements then increase that by 25% to determine the size engine needed.
Fast recharging will also require a bigger engine because mower alternators are not particularly efficient .
The actual standard for measuring Hp changed a while back which caused most engines rated Hp to be diminished.
Go to Small engine warehous or Small engine suppliers and see all of the engines wit a note they were formally rated 2 to 4 Hp higher.
Also there is a big change in expetations.
Back in 1966, the oldest ride on I still use daily, mowing 1 acre / hour was increadible and 2 hours would be fantastic & 3 hours acceptiable .
Now days because of all the labour saving devices liberating so much more time we want to be able to mow 5 acres an hour and mow our entire yard in less then 5 minutes because we cant be on face book while we are mowing so might miss a vital photo of a woman in a short skirt showing an 1/8" of panties or a lunch one of our fake friend posted.
Instead of being an enjoyable experience of time to oneself where one can think & relax it is now a chore to be done in the absolute minimum time.
And of course, grass has to be cut WHEN I WANT TO cut it , so leaving lawn cutting till late evening when it is best & easiest to do no longer happens.
Then here is the ego thing, if the person I paid to mow my grass was riding on a 400Hp turbo charged mower with a 200" deck then I need to have a bigger one.
I mow 5 acres with an 8/30 and a 10/34 if there has not been a customers mower to field test and very few modern mowers would be more than 15 minutes / acre faster.
In fact some of the Husqvarnas are slower than my 60 year old Rovers ( excluding ZTR's of course )
Professional mowers are of course different, wed, dry hot or cold, every week is every week and for them time IS money so overpowered mowers are worth the extra cost & fuel