Again there is a lot of variation, Was talking to a dairy farmer the other day who uses nothing but Ding valley Noah straws and has very few assisted calvings,there again, the calf is a necessary by-product of dairy farming, might be a valuable one, but the important bit is getting the cow i/c. Big cont calves, might top the market, but they don't all just flop out the cow, you have to factor in the effects of hard calving, RFT and 'dirty' cows as an example.
last really bad calving here was an angus cross heifer on to an angus AI bull, dead calf and we sent the heifer on, that was several years ago
We had Hford bulls before we went to Blues and if anything find blues more easy calving though there isnt much in it and the switch put our store sale price up by 20/25%, lim stores would be similar money but chalk and cheese to work with