What I have found after having a power Meter fitted to my bike is that my optimum cadence for making the best power vs getting fatigued is around 80 to 85 rpm.
As with you I always tried keeping a higher cadence before working with power but now I do have a power meter is not a matter of guess work anymore. All the data is there in front of me to analyse after every ride.
I once tried a high cadence turbo workout of one of them YouTube videos, I purposely didn't look at my power during this workout. I averaged 103 rpm for 45 mins and I can tell you I was knackered getting off the bike. My avarage power was only something like 210w. Normally, by varying the resistance and keeping cadence around 80 - 85 I can do 250w comfortably for an hour on a turbo.
I know we see pro's on the TV spinning like mad, and for them this is efficient as they have the fitness to do it. For the likes of you and me though I wouldn't get to hung up on keeping a 100 cadence as this almost certainly won't be your most efficient cadence IMO.