Just out of curiosity, what kind of RPM's are you running while headin down the freeway at 70MPH?
At 70 I was at a nice even 2500 RPMs. Of course the gauge might not be perfect.
I only ask because I think it was revving higher before I replaced the plugs and wires.
Bosch +4's and some Aurora custom made 8.5 MM wires... Love the difference they made immediately.

 

I dont drive 70 so I cant tell you on that one.

Plugs are wires have zero to do with engine RPM, the engine will turn at "X" RPM at "Y" road speed solely because of gearing in the transmission and differentials.
Plug wires deliver the spark, the better the less resistance in the wire the stronger the spark.
Spark plugs burn the fuel, the better the burn the better your MPG, nothing else changes.

 

2500 for me

 

about 2400-2500 at 70 mph. but like spike said, I don't drive that fast. I cruise around 60ish for the mpg boost. I get a happy 15mpg on average.

 

Exactly.
Saves me $20 a week in gas on average and add's only 5 min to my commute each way.