I don't think you've gained pressure. Pressure is usually constant throughout the system. The biggest change when increasing the size of your water pipes is an increase in water flow. If you knew your water pressure before and can check it now with a pressure gauge on a hose bib it would help determine what it was.
The size of your main water supply line, incoming pressure and water flow are the main variables used when designing a sprinkler system. When you change the main water line, your sprinkler system goes out of whack.
If you're not able to dial down the nozzles further you can replace the nozzles with ones that have a smaller radius. They're fairly cheap and easy to replace. You don't need to dig out the body, just pull up the pop out stem, unscrew the old nozzle and screw in the new one. Most come in standard sizes but I have seen some orbit ones that are larger. Some have female threads others male threads so be sure you know which ones you'll need.
Replacing the main water supply line isn't something people look forward to doing. I'm guessing you had some issues at some point with low flow/pressure caused by damage/corrosion to the main. The previous owner might have had the same issue and decided to replace the original nozzles with ones that have a larger arc to compensate. Now that the water issues have been fixed they need to be changed again. Just a guess.
I don't have my own system but help a relative maintain his. If I ever do install one the main reason will be to use these Hunter MP Rotator Nozzles which I posted some info and vids of on my blog. I think they're really cool.
You may also be able to install some sort of flow restrictor before your main valve box but I'm not even sure such a product even exists or is easy to find.
Edit: Forgot to add... If you want to learn how to design, install and maintain your sprinkler system read everything at http://www.irrigationtutorials.com/ I read it virtual cover to cover because I wanted to install my own sprinkler system after seeing the MP Rotator nozzles. (Seriously, for me it's like they shoot out little streams of happiness :) I never wound up installing one but I learned enough that when my relative has a problem with his I can go over, identify the problem, find the right parts and fix it. If you want to learn everything there is to know about your sprinkler system. Read the articles on that site.