In light air you will definately go faster with the jib. In medium air you will be faster with the jib too, only in big wind will you be better off to leave it in the box unless you have crew, then take it. I assume you have a self tacking jib. It's very easy to trim it and forget about it in the tacks even if you are sailing alone. BUT, when you raise up the spinnaker, be sure to let the jib out quite a bit so the air can freely pass through the slot.