Heck, let's say bike equipment is "equal" as well. Pick a lengthy hill you are used to and ride it in a normal steady fashion you are used to. Note your speeds, time, effort, etc. In a couple day repeat that same hill with the same kit on except for an additional 10lbs of lead weights in one of your water bottles (an old no longer used one). Record all the data and compare for yourself. Of course it will be a somewhat imperfect experiment but it will be accurate enough to give you an answer...

BTW - come back and share your finding when you are done!