Thank you gentlemen..............the story develops ?
GBZ, if me memory serves me right, the term "unstick" is only used for tail-wheel aircraft ?
Sycamore, The assumption is the same everything except weight
AAN Having got airborne (lift exceeding weight) I seem to remember that acceleration - and therefore ROC - is a function of thrust compared to drag which will obviously be a much greater margin on the lighter aircraft since drag is a combination of lift (induced drag) and speed (profile drag)
Birds.........I'm sure I saw an Attenborough programme showing Vultures that had eaten so much that their weight was above RTOW and they had to wait for a reduction of OAT in the evening to get airborne. (Having operated in and out of Africa many years ago, I sympathise with their problem !)