It's been a while but it seemed to me that high ISP isn't very big win for the first stage anyways. Basically linear with everything being equal which as you me

It's been a while but it seemed to me that high ISP isn't very big win for the first stage anyways. Basically linear with everything being equal which as you mention it isn't. So slightly lower ISP means slightly heavy first stage. Either way it's disappointing NASA is determined to keep the Space Shuttle's white tech elephant going.