Romax,
We used Gigolo Joe on Hereford x Shorthorn cows this year and our birthweights were between 85 - 95 lbs (Of course, our Canadian winters tend to add 10 pounds to an American birthweight), as does using him on cows. I wouldn't hesitate to use Joe on heifers, as they were moderate enough in their bone size and were pretty consistent in type. The semen quality was also excellent (AI'd nine cows and got nine calves). I've attached a baby calf pic, although its pretty early to judge them yet!!!
Another bull who's semen is marketed in Canada and we have had excellent sucess with (We breed ALL our heifers to him every year) is Daines Thriller. He is a purebred, homozygous black Maine who's calves average about 84 lbs at our place (We've probably calved out close to 50 of them by now and they've ALWAYS been born easily). They get up and chase the heifer around the pen about 20 minutes after being born and we've had some highly marketable calves out of him. (Attached a picture of the steer that was Reserve Champion Prospect steer at Agribition last year - He was a Thriller steer).
I don't know much about Tyson yet, but I would also be interested in hearing BW, etc. on him. We are a bit more limited in what we have available up north, which makes finding the right bull that much more difficult!