They come from mercury with the jets already attached and carry the full mercury warranty. They have the medium jet on the 60/40. the 40 EFI jet has the same displacement as the 60 EFI motor. Both are 4 cylinder also. The mercury website is very confusing to say the least. If you think Troutt and Sons don't know their business, call outboard jets direct and ask them. I did with a technical question about boat and motor configuration and they referred me to Joe Troutt!
By the way, The jet is the same size as I had on my old OMC 40/30 jet. The 40/30 2 stroke could not keep up with the 40
merc 4 stroke. My nephew has my old boat and we have run side by side many times. If the 40 merc were 40/30, the OMC
should be able to keep up with it since the OMC is on a lighter boat. It can not. It is about a 25 MPH boat. My heavier Alweld is a 31 MPH boat with the 60/40 merc.
The 4 stroke on a jet is not much quieter than a 2 stroke if any at all. The sound is deeper. It is nice not to have to mix fuel in a 4 stroke and the mileage is noticeably better. Warranty is better on 4 stroke. Downside, 4 strokes cost more, are heavier, and don't have as quick of a response.
I am not a mercury fanboy by any means and owned a small chain of boat dealerships for years before selling out. I have run most everything. If you are looking for ultra low maintainence go 4 stroke. If speed is your need 2 stroke is what you're needing.
Sorry so long winded. Hope this helps.