If you're talking about the Model 75 made by the Sharps Rifle Company, only two made it to completion with only one known to be in existence.  (Sellers, ch.15)  Looking at a picture of it, it looks unlikely that it had a through stock bolt.  If Creedmoor is asking about the 1875 model made by C. Sharps in Montana, then it's possible that it does have the through stock bolt.  I've seen several but can't remember if it had tangs or not.  Either way, they don't hold a candle to an 85' highwall for ease of shooting or cleaning.  As far as strength goes, they are probably similar.  Highwalls are pretty easy on parts except for breaking of a firing pin or possibly a mainspring.  C. Sharps should have all parts available.  Bob

Howdy from one of the the newbies on the block in Missouri!  I own both a C.Sharps Arms 1875 in .45-70 and a Winchester (new model) 1885 HW in .38-55, among other things.  I can tell you that when I am practicing my dry-firing with a snapcap in the chamber, the hammer fall of the much heavier 1875's hammer noticably pushes the muzzle down when holding offhand, compared to the much lighter 1885's hammer.  This is bound to have some effect when actually shooting.  I don't shoot competitively, so won't comment on what that might be.  
Don't misunderstand, I have great affection for, and enjoy both rifles very much, but there is definately that one difference between the two that is very apparent when you have both rifles right there side by side to compare and contrast.
Best regards.

Here's my two cents worth,

I have two sharps rifles,both 1874 in 45-70, and one Uberti High wall ca 38-55.  I have fired way over 40,000 45-70s, the vast majority in the two sharps rifles, and the rest in a few trapdoors. Thats a lot of shooting, and there were some pretty good groups in there, and I am very satisfied with both Sharps rifles. HOWEVER: I can tell you from first hand experience that what you read about the weaknesses of the sharps (extractors and firing pin) is true. I have had to replace several extractors and a lot of firing pins. Both had the old stlye one piece firing pins and they are a pain in the butt to fit when you need a replacement. I eventually put a Pedersoli breechblock in and converted to the two piece firing pin., and have broken a few of those but they are easy to replace.  I have not fired the High wall enoug to testify as to its durability but the design of the HIgh Wall is light years ahead of the Sharps, a true genious at work!
I like them both a lot, but if I had to say which is the better design, its the High Wall.   On a related note, I have fired quite a few rounds through several trapdoors, and NEVER had a problem with any of them.  A very simple, effective and reliable design, and the original are all very well made.  When tuned for target shooting, can hold their own with the Sharps! Just my opinion, fwiw Joe S