The Buderus is a little more efficient than the Biasi, in general. The Biasi B-10/3 has a lower firing rate than a G115WS/3, so there could be some savings. The B-10/4 has a higher stack temperature than the G 115/3 which will make it a little less efficient. Not clouding the waters all are great pieces of equipment. The real key is sizing the equipment to the load. Depending on the load I would use a B-10/3, then a G115WS/3, then a B-10/4, then a G115WS/4. Point is figure out what the real load on the equipment is.
If the load is really 55,000BTU's a B-10/3 will work.