The bus journey from Sucre to Tupiza is meant to take about 8 hours according to the Lonely Planet, closer to 10 according to Footprint and, crucially, about 8 hours according to the woman I bought the bus ticket from, who works for the bus company - she should have a fairly authoritative figure.
Imagine my surprise at being dropped off near Tupiza (the bus driver didn't want to drive the extra 2 min to the bus station for reasons that were never explained - I, and the others who got off the bus, were more interested in the question "is this Tupiza?" as the bus driver had pointed across the river and said something about taxis and Tupiza, not quite what any of us were expecting; but it turns out her was just saying this is Tupiza and if you need a taxi they are on the other side of the bridge) after just 5.5 hours total time, including good 20 minute break for "lunch" at around 11am.
I thought the driver was being a little enthusiastic with his speed on some of the roads, but shaving over a quarter off the total journey time is interesting.
Bolivian buses - they're late, apart from when they are very early.