Today's "show" Labs IMO don't reflect the breed standard and have gotten away from what they were bred for, and that was a days work in the fields. Most of the show dogs I see get winded running once around the show ring. They are too heavily boned, deep in the chest, short in leg, the heads in many cases look more like Rotties. I can't ever imagine these dogs doing 20-30 retrieves in a day.
Brooks, my 6 year old yellow boy, is too me anyway, the classic looking Labrador. He looks very much like what you would have seen in the show ring 40 years ago. He's fit and athletic, and can literally go all day. Brooks weighs a solid 78 pounds, and is just at 24" tall.
Rose is the exact opposite of Brooks. She is 100% field bred, she very fast and has tremendous amounts of drive. She will run multiple marks in the 200 to 300 range and will be going as hard on the last one as she did on the first. Rose weighs a muscular 56 pounds, and is about 21" tall. She's about 16 months old, and I don't expect her to get any bigger.
Song is bred from British field lines, and based on how his father and brother look, I expect his to be a slightly smaller version of Brooks. He's only 3 1/2 months old so there's still a lot of growing to do.
He is a pic for comparison.