I use the "memorize the tempo of songs you know well" trick and I also use Arky's "what do double stroke rolls at 200 bpm feel like" method. Funny how we find our own way to these same weird things sometimes.
Using our personal strengths/limits/memory of how we play would seem like an effective way to know what speed a song is, but that ability is affected by the things that also affect our perception of tempo, such as fatigue, anxiety or excitement, effects of alcohol, etc.
So if you know that a song goes as fast as you can play 16ths with one hand, that's great...
under completely normal circumstances. You silently play the part on your thigh so that it
feels right, and you're good to go, right?
Suppose it's the end of the night and you're tired? Suppose it's the beginning of the night, and you're nervous or excited or have a little extra energy? Suppose that, over time, you become able to play faster? Suppose you have an injury, and can't move your hand that quickly?
For all of those common scenarios, the ability to recall a tempo by first
playing it, is undermined. There needs to be a method less susceptible to the physicality of playing, and memory is less likely to be affected (except possibly by alcohol.) Ultimately, if tempo is that critical, a metronome needs to be used, not as a click, but to establish the desired tempo to start a song.
Are tempos really that critical? Some more than others. We all know that some songs seem to sound great in a range of speeds, while others are obviously too slow or too fast. Even if a song is played perfectly, it can easily lose its feel if it strays too far from a working tempo. It can affect the dancers, it can affect the singer, it can affect the other players, and it can affect the drummer, even if they counted it of in the first place!
I had one band where all songs were assigned a tempo, and I used a metronome to get my count for those songs (after which it was my job to hold that tempo.) I loved that system! There was never any doubt as to whether I had counted off too fast or too slow, and we knew that the songs always sounded their best. well, at least in terms of the tempo.
Bermuda