Irish Sport Horses, and Oldenburgs, are not a really specific breed, but rather a recognzide crossing of breeds. I mean, Oldenburgs can be part this and part that and still be called Oldenburg. Like part Thoroughbred, part Hanoverian and part Swedish Warmblood. At least that's what I was told, and I will accept correction if that is wrong.
Irish sport horse I think is Irish Draught crossed with Thoroughbred, or something like that, such as Selle Francais or a lightwarmbood.
I have the fortune to part lease an Irish Sport horse., He is half Irish Draught and half Selle Francais. He has THE best temperament of any horse I have ever ridden. He is brave, willing, has a ton of "try" in him and is very trusting and gets along with any horse, any human. He jumps well, is fast at times and very surefooted. What more can you ask?