I’ve got to chime in here as I did what some obviously wouldn’t do. I did it deliberately. I put a BIG, well-bred Holsteiner mare to a Thoroughbred to produce an upper level jumper. The result is an improvement on the dam. She’s a better mover, typier, better conformed, prettier with a fabulous brain and work ethic. With respect to size, she is smaller in height and mass than her mother, which is consistent with the numerous Coconut Grove offspring I’ve seen. I’m sure there are exception, but it is worth pointing out that size conclusions with the Coco’s should not be quickly reached based on their initial foal growth. The ones I’ve known have put on a lot of height in the first year and then slowed down considerably.
My mare is currently with my trainer who was an International Grand Prix rider and Nations Cup team member for many years. He has ridden some of the greats including Ramiro as he rode for Fritz Ligges during his career. He has compared her to one of his best Grand Prix horses. There has been no loss of scope with this cross, rather, I now have scope in an extremely athletic and adjustable package that most definitely will be extremely competitive on today’s more technically demanding courses.
Since I touched on scope, the mares by Coconut Grove that have done the jump chute during AHHA inspections have gotten stellar scores of 8s and 9s. I know Bent Hickory (wish he’d chime in) has a mare by him that was accepted in the Hanoverian JBP with extremely high conformation, movement and jumper scores. She too is an improvement on the dam including scope. In the less than 10 years that Coco has been available, he has been the choice for top breeders, top GP mares and top GP riders. His offspring have been exported to other countries and I know of one semen broker in Scotland that likes them so much he’s breeding his own mares to him for upper level jumpers.
I think there have been some good TBs named here as that was the request of the OP. I don’t think that putting a TB like Coconut Grove to a mare such as the OPs is the kiss of death for an upper level jumper. It’s not unheard of. Coco was never bred till late in life and he’s an grand old man now. Time will tell.