Biggest determining factor to value is condition. That said, if you have two model 92's of exact same condition, one a rifle the other a carbine, then yes the octagon {rifle} is generally worth a little more as there were fewer rifle versions of the 92 made. It is also more rare in a 92 as most were carbines. Also have to consider who is buying and what they want. While they definitely made more carbines, they seem to be the guns most used and are therefore way more difficult to find in really nice condition. While fewer of the rifles with the longer octagon barrel and crescent buttplate were made, it is usually easier to find a nicer one of those as they were bought for a hunting rifle and treated gentler than a saddle carbine carried and typically used as a tool.
