But to answer the OP's original question I feel yes 18 seer is overkill, but of course that's just my opinion as you will find many opinions here, personally I think when they went past 10 seer it all went down hill. but you can thank your Daddy Uncle Sam for that move.
__________________________________________________ _______________________
Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill