I cannot really speak towards the PSI or GPM differences of foam cannons, as I have certainly not tested enough pressure washers or foam cannons to provide any empirical evidence.
I can tell you that I have an AR Blue 2000psi (1.4gpm) and I attempted to use a cheap foam cannon from Amazon (
the Dusichin that they have as their best seller), and while I was able to produce what I would consider "decent" foam, it is certainly not what I see in some pics and videos on youtube. I started with probably 4-5oz Megs gold class in the bottle, and have ended around 7oz. I found that I actually got better foam as the volume of liquid in the bottle decreased as well, but I did not experiment further.
I washed a couple of cars with it, and last week ordered the MTM low PSI version. I have not had a chance to use it yet, but from what I can find it has a smaller orifice (.1.10 vs 1.25mm) that is supposed to make it well suited to electric pressure washers.
Since you have not bought, and it sounds like you are willing to spend the ~$60 for an MTM, why not go ahead and get the low pressure version to start?
https://www.amazon.com/dp/B00EDSLVQC/ref=cm_sw_r_cp_apa_1KCsxbAX5YV1X
Note, it did come with a standard 1/4" quick connect in the package.
Or, if you already have one, you might consider a new orifice from MTM to see if that helps. I might do that myself, once I have some time with my new cannon, and verify that it fits between the two.
https://www.mtmhydroparts.com/colle...oducts/foam-cannon-nozzle-replacement-orifice