All i know is on 6-6.5g rollers i dont get to 7000rpm. Prob would evenuallly hit 7000rpm but i dont have a long flat enough road on my commute to get this. Couple of downhils it did get to 7000-8000 but rarely if ever on flats, and thats with the stiffer spring which like you say raises the rpm.
Now with the 1500rpm spring and 5.1-5.3g rollers it stays pretty much between 6800-7300 rpm all day, even up hills.