Yeah, it could totally be your perception. Two other things that could result in perceptual errors relating to stiff racquets are dwell time and shock, which are related. When the ball impacts a stiff racquet it will stay on the strings a shorter amount of time. The briefer this "dwell time" the greater the shock transmitted to the arm. In their books, Cross and Lindsey hypothesized that players associate brief dwell time and greater shock with fast shots: The ball is on the strings for a shorter time and the brain interprets this to mean that the ball rebounds with more speed as a result. But this is akin to concluding that because a train stopped only briefly at the station that it then left the station with greater acceleration. Also, the brain may interpret the "crisp" shock of a stiff racquet as indicative of a fast shot. The impact felt violent and forceful, so the resulting shot must have been very fast, right? But as the data shows, the actual difference in shot speed is very small. The difference in shock might be great but the difference in shot speed is not, at least that's what the data says. I think it's likely that our nervous systems are better at gauging shock at the hand, wrist and elbow than they are at accurately judging shot speed, particularly as it seems very difficult to isolate speed from a shot's angle, trajectory, spin and depth. On the other hand, the physics of racquets, strings and the players using them turns out to be surprisingly complex. It could be that further experiments will turn up some error and we'll then hear that stiffness is more important than the current experimental results show. But without some new experiment, we're left with what we have now: the results of various experiments showing that stiffness doesn't make that big a difference in power, and the generally held perception by players that it does. I tend to trust data acquired in controlled experiments over my own perception because I know what a knucklehead I am, but I also don't think subjective perceptions should be ignored.