Selection of Right Transformer

Calculating by total connected load is conservative, but it may be too conservative if the concurrent loads are much less, as seems to be the case here.

For a small-scale example, I deal with refrigeration systems in which a control transformer might have six solenoid valves per zone as a connected load, but only two at a time might be energized as a concurrent load.

It can be tricky in such cases to determine the "worst case" simultaneous load.

It is a good design practice to apply Simultaneity Factor (How many loads will be ON simulatneously) & Diversity Factor (What is the ratio of Running Load vs Connected Load), while sizing Transformers. I am surprised how you missed that. Else, this - Oversized transformer - will be the price you will have to pay.

Since transformer is stationary equipment you need not worry too much regarding its efficiency. It gives best efficiency at 50% load connected to it. it means you get 99 % efficiency at 1250 kva load. or may be 96-87 % efficiency at 808 Kva load which you are talking about. Moresoever, transformer is designed for maximum load connected to it.

You don't have to worry unless you are paying the power and cooling bills I guess. In my location at about 10 cents/kWhr even the cost of losses in large transformers can account for tens of thousands of dollars per year!

Did u apply the diversity factor while calculating?