I have all mine on pasture nuts fed with sugar beet and alfalfa, incl my sisters ponies and my own competition horses. I havn't found them to be overheating and they are all looking really well on them.
I used to feed my Welsh cob cross on D&H pasture nuts and also used D&H pasture mix sometimes, but never found them to be heating. Mind you, he was so laid back he was almost horizontal! I had him from a foal till he died, aged 12, from grass sickness.