BT 80 - 2.6" clustered rockets fly fine on D12-5s as they are the recommended motor for a number of kits, including a number of Launch Pad kits that use light parts. Build light and strong and you will be fine. The Perseus uses only two D12-5 as dose the Scimitar with even more drag. TLP Nike Ajax on 3 D12-5's. The weighty Roachwroks Nike Hercules uses 4 D12-5's. The ASRAM uses two D-12 5s, but will fly fine with two D12-7s! How do I know this? I have flown these rockets many, many times and look - no zippers or massive damage!
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Looks like you are flying an extended Perseus, like the one on the left. With 3 D12 motors, like an F 36, and basswood fins you will be fine on a 3 or 5 delay in good conditions.
Label papered balsa is lighter and just as durable and easy as basswood.