The reason I am looking for the lightest setup is I hurt my knee and it would make things much easier to maneuver with it being lighter.
If you are using proper technique... the differences in ease of manuevering would be minimal. If you are not using proper technique... you were probably straining/tweaking your knee... setting yourself up for an injury.
I would dump the money into physical therapy... with regularly strengthening and conditioning - you should be able to double the strength of your knee stabilizers... but if you were to buy the lightest board and bindings... at most you would probably drop the weight be 10-15%. I say this after having an ACL tear (someone crashed into my knee in ice hockey and 2 MCL tears (binding broke on a landing, crashed riding a chute and hit my knee on a rock spire).