Think of it like a manual transmission on a truck. The higher the gear, the faster it goes but the less torque it has. Same thing with changing out the sprockets. A 7-pin will give you a lot of torque/grunt in the cut, but chain speed will be slower than an 8- or 9-pin. Leave that long bar on and switch to an 8- or 9-pin, and chain speed will increase, with a resulting loss of torque.
The 880 is designed that way with the 7-pin because it's a very large saw meant for bucking and felling very large trees, so it has to maintain that torque with long bars buried in big wood.
You can surely put a shorter B&C on it and run an 8- or 9-pin sprocket, which will give you more speed and maintain torque. But why would you? It would just be a really heavy mofo cutting smaller wood. Best IMO to let the 880 wear its 48-inch bar (or longer) and do what it does best, and run 60-75cc saws in smaller wood.