LOL.... I actually do design antennas for a living. I've been employed in antenna designer for 27 years, and before that, experimenting with ham antennas since I was 16. I have worked on everything from shaped-beam reflectors for communications satellites through land-based electrically small HF antennas.

My bottom line is this... I can't even begin to tell you how much shortening the antenna will reduce your range. There are too may variables to even guess. You have to try it and then range check, range check, range check. Don't assume that buying a commercially made loaded whip is better than just winding your own. Range check them as well. Don't assume that the receiver front end will tolerate a wide variety of impedances, length is length and it takes length to produce voltage. And don't assume RC-CAM's data is infallible. I'm not so sure his experiments are all that clean.

Range check! The best range check is a comparative one where you compare range with a full antenna to that of the shortened antenna.

End of rant.