If the other folks on this supported ride are using race bikes, and you are looking to make it easier to try to hang with them in 20mph plus pace lines for example, I suggest *temporarily* changing out your OE stem to one that drops the top of your bars down below seat level similar to the level that you found reasonable on your missing, fast road bike. This will reduce frontal aerodynamic drag, which is an increasingly important factor at higher speeds. It will make a notable difference at higher speeds.

If your supported ride is a multi day ride, and you don't have much time to try out the new stem in advance, take along your original one in your luggage in case the new one doesn't work out. If it is just a really long, one day ride, be sure to try it out before the ride. JMO.