It is useless to discuss the relative "efficiency" of inverters without regard for where on the efficiency curve you are on each inverter with a particular load.
If every inverter had the same sort of curve, where at 3/4 it was at max efficiency and you had a 300w load, you would choose a 400w inverter, not a 300w one even though it would run that load (assuming continuous = rating, not usually the case)
If it comes to running an 80w TV on an inverter, either a 300w or a 2000w inverter will be inefficient, but the 80w is higher up on the 300's curve than it would be on the 2000's curve.
I ran a few tests of that a couple years ago and posted the results, but can't find my notes on that. Could be in the Forum archives somewhere. ISTR the same 32" LCD TV was making the inverter draw 8 amps on the big inverter and only 6 amps on the smaller inverter.