The SXT is a shorter version (14") of the extreme riser (16"). The ZSR is a shorter version of the standard riser. The standard style riser is more traditional in appearance being swept back into the limbs a bit more. The extreme style riser is deflexed forward slightly, giving more of a power stroke to the shot. I have shot a SXT, Extreme, and Standard. I like the deflexed Extreme and SXT the best. I own an extreme and have a SXT in the works. The grip is phenomenal. Quiet, Fast, and lethal. Great design, and great people to work with. Give Bill and Tracy a call, you won't be disappointed.