To be honest, I've never actually raced a crit or rr where the overall pace (not surges) was so wildly fast it put the field in stress. For the most part they've all been 25-26 with surges to 30 for the purpose of closing breaks. Fastest I've probably been in is the practice crits we've done around 28.
I'd love to be a crit where the pace is so frantically fast that's actually a factor and its not just everything being neutralized up to the sprint. In the 4's that's a tough ask though.