Simple low Voltage Transformer Question

[JohnQPublic]

Hi, Hope someone can help? For weird reasons I want to use an MR16 50w downlighter lamp connected to a transformer. Due to circumstances, once in a while I may want to change the bulb to a 75w, but this may be once in a blue moon !

So I have the choice of 2 transformers, 65va or 105va, of course if I choose the 105va then I can chop and change bulbs as often as I would like to,(as the mini/max load range is 35w-105w) however with the 65va I cannot connect a 75w: Question: "If I decide just to install the 105va and run a 50w bulb from that, would I be using up unnecessary power from the mains?, as I know the bulb will only demand what it needs, 50w, but would a bigger transformer all be it not loaded to the max, maybe burn more lecy from the mains? Or would it be overall cheaper just to install a 65va transformer?, I understans there would be heat losses from the coils but surely not enough to pump up the bills!

Thank you anyone?

[sparkysi]

Im going to assume your using an electronic transformer rather than a wire wound. If so, fit the 105VA unit and forget about it, it will be fine and dandy.