I have owned five double rifles, and eight drillings, eight over and under and side by side combination guns, as well as a bunch of over and under and side by side shotguns. Ive shot them all, a lot. So I have some experience with both single and double trigger guns.
I prefer guns that cock both barrels on opening,; i am not a fan of recoil coking mechanisms.
I have never liked double triggers. I have never developed the smooth change from front to rear trigger. So, I am a slow second shot with them.
I would point out that you need to come back down and require your target before you fire the second shot with heavy recoiling rifles. They are different than light skeet loads.
I have doubled a number of times on hard kicking double trigger guns. That is, i believe, the fastest second shot you can make. When I've doubled, the second shot went way high and off target.
A truly experienced double rifle shooter, with a perfectly fitting rifle, that the shooter is thoroughly familiar with can be quite quick with either. If any of those 'ifs' are missing the follow-up will be slower.
Just my experience,
Bfly