And my experience is that you can actually get well beyond the official lengths for most signal types even with comparatively cheap cables as long as you're willing to test and throw out the odd cable or connector. Standards are written with conservatism in mind.

In most cases, you're right. The vast majority of switches use a sore-and-forward design (buffering), but when you get into latency-critical applications, another type of switch design is used, typically called a cross-bar switch.

http://www.researchgate.net/publication/220055485_A_low-late...

http://www.google.com/patents/US5339396

I think opinions vary on whether or not crossbar designs "buffer" but it mostly depends on how you define buffering. None the less, the low-latency crossbar designs try to eliminate the latency caused by buffering in the older but more common store-and-forward designs.

This sort of thing is designed with a very, very comfortable margin. I'd expect if you wanted, you could get quite a lot beyond the rated maximum.