generally horse breeds in endurance results are simply listed as, Arab X,, which could mean anything. The way arabians register half arabians even though against the rules, alot of the Half's are registered arabian crossed with unregistered. I've also looked at half arabians that were 7/8th arabian 1/8 saddlebred, or was it standard bred. Whats a NSH again?
If I was breeding for Endurance, Id pretty much just look for a big arabian of crabbet or Polish lines. Looking at Tevis results you see a handful of other breeds, so would probably look there. TB, Morgan, saddlebred, a true Appaloosa, not just the colored QH stock, NezPerce horse.
Currently I am sitting on two nice Walkers, and can really only keep 2 horses. I want a big Arabian or an at least 3/4 arabian, but can't get one unless I trade/sell one of my Walkers, Soooooooooooo I am campaigning a TN walker at the moment.