Carbon and construction,Formula Excel are a glass/wood limb and Formula 720 are a carbon/wood.For recreation both will do fine,the 720 may have a slight performance advantage with the carbon.The 720 limbs also come in an ILF version,if you get the 720 make sure they are for the Formula series.Also those limbs are rated for a 25" riser so on the Buffalo's 19" riser it will add around 6#.So to get around 30# you will want 24# limbs to give you around 30# or so.Maybe look for some 30# or 35# Buffalo limbs,Buffalo limbs have carbon in them.