It seems like the title of your thread should have been " someone PLEASE convince me to go SR20 "
seems like your heading that way, so i'll try to convince you.
Ive had an S14 SR20DET before, and finding parts isnt hard at all. You can cross reference lots of engine parts (even internal parts) from the USA from the SR20DET's cousin, the SR20DE. There is also PLENTY of aftermarket support for that engine, which you probably already know.
Fuel consumption is one of your constaints, and I can tell you In My S13 w/ SR I averaged 26 highway and somewhre around 18 city, and thats driving lead footed here and there (the way we all drive!).
I Havnt driven any Sr powered Z's but i can tell you that my S13 ran consistent mid to high 13's on street tires and at 3000 ft elevation.
You put that kind of power in a smaller mass Z and all the numbers just get better.
However, if you do go that way, May I recomend getting an S14 SR. bigger, ball bearing turbo, VTC , better intake manifold, and easier to work on.
hope that helps.