how many rpm's will i drop going from 3.91 to 3.55????????????????

i used to do 2-3 hour cruises on the highway with 3.91 and 3.55 gears.. sure the 3.55 took the edge off some but it still wasn't good for the speeds i wanted to cruise.. i guess if your only doing one or two long highway cruises a year 3.55 will be fine but for me i went to a 2.94 and really liked them. in the end i still wanted OD for the highway with the 2.94 gear..lol
I did just that today. With the overdrive and 3.73 at 75 I was turning about 2500. Now with the 2.94 at 75 I'm turning 1900. This is with a 26.5 inch tire. Should be able to cruise all day now lol