I believe 3 buffers is the minimum you need for the CPU and GPU to be able to work independently and never wait for each other. Sure, one could queue up a bunch of extra frames and you'd have more margin in case of a multiple frames long stutter (at the cost of a lot of input latency), but you're typically better served avoiding multiple frames long stutters if possible. Triple buffering is, I believe, more about squeezing out all the performance you can from the hardware, not about just queuing up some number of frames which happens to be 3.

Adding some detail to this: With three buffers, you have one front-buffer (what's currently visible on screen) and two back-buffers. Let's call them A, B and C, respectively. This lets you work on the next frame in, say, B, and when it's ready, you queue it up for presentation. At the right time, then, the roles of the buffers will be switched, making B the front-buffer and A a back-buffer.

The third buffer comes into play if you want to start working on the next frame _before_ the switch has occurred. So you start drawing in C, and if the right time should hit, the display system can still flip A and B. In this case, triple buffering gave you a head-start with drawing the frame in C.

Going further, if you complete the frame in C still before the A/B switch has happened, you queue up C as the next frame, instead of B. Then, you can start working on the next frame again in B. With this scheme, there is no sense in having more buffers than three.