The OP asks if there are any "real benefits" to thumbhole stocks. The answer is a definite YES so far as competitive rifle shooting. Though thumbhole stocks may seem relatively new in the world of hunting rifles they have certainly proven an advantage in three-position international style rifle competitions. Many years ago when I was a member of the US International rifle team shooting against the Russian team, when was then the world's best, and consistently beat us in skill, coaching and equipment, I bought one of their thumbhole stocked rifles when we were shooting in Moscow. I used it at the time in some 300m matches but good ammo proved a problem so it was retired. I still have it, as shown in attached photo. During that period I also used a beautiful .22 RF Hammerli rifle, which has probably the most beautifully styled thumbhole stocks of all time, which I still have, as shown in attached pic. Also attached is page from 1960 Stoeger catalog showing Anschutz target rifle with thumbhole stock from from that era. Note the price, which seems cheap today but back then it was more than $100. more than contemporary rifles by Winchester and Remington, which did not have thumbhole stocks. As we now know, the Anschutz soon ruled the target game, with one main reason being the advantage of their thumbhole stock.