Nah, it might actually be fewer than 4 years for you, since you have more cold which tends to be a precocity inducer. The guys in california get fruit within a year or two. The tree is a vigorous grower, but it won't flower until it's either mature enough or stressed.
Lemon zest fits the bill. It does take 4 or so years to come into production though (here in FL).
Don't say that, just put one in. Probably means 6 years for us, although I do have a few rocket fuels in my tool box to help speed things up. 
I agree with Cookiemonster, I have two Lemon Zest trees on florida Turpentine rootstock that are starting their second year in the ground and one tree held several nubbin fruit the first year and the second tree is holding lots of thumb sized fruit this year. The canopy is only about three feet wide and I go by the Japanese method of allowing approx 60-80 leaves for each fruit to reach optimal flavor and sweetness so I'm only going to allow my tree to hold 2 fruit. This tree is planted very close to my house so I purposefully want to stunt its growth by allowing it to hold fruit.
But anyways, Mark, I think with your knowledge of plant growing and your relatively cool winters, you may get fruit within two year if you allow it. I hope you will be pleasantly surprised with the super awesome flavor of the Lemon Zest, it's absolutely incredible, one of my all time favorite mango varieties.
Here's a few shots of my young Lemon Zest, I'm sure more of the fruit will drop but if it doesn't soon, I will thin it down to a couple fruit. Here's in California and I assume other areas that are cooler, even some of the low producing mangos can be very highly productive like Eunices Edward tree that produces hundred of fruit.
Simon
