Value of a knot

I got an idea from a recent thread.

I would like to know what you guys would spend to go a little faster. This
would seem to be interesting information, and a fun topic.

Please note the present speed of your plane, because 5 knots means a lot
more at 100 than 200.

Personally, It seems to me that a speed mod less than $1,000 a knot is
likely a good deal. I presently fly about 142 in a hurry, and 120 when I am
not.

I know the people selling the mods often over advertise, but lets assume we
know the real increase of a given mod from an expert. What's it worth to
you?