Even not knowing all the factors such as part of the country, insulation, glazing, room orientation etc., if 6500 btu's did the trick don't get a bigger unit. 10,000 btu's is overkill and will result in poor humidity removal/higher relative humidity. Don't do it!

Thank you!

I see some 5000s and 6000s. If yours was keeping you plenty cool on the worst days, you might consider going down in size. Was the 6500 cycling on the hottest days?

I notice that the newer window units typically have the blower set to run continuously, even when the compressor is not going. That tends to increase humidity. That can be bad in humid climates. Look for a model that allows you to run the fan only with the compressor. This is sometimes called an "economy mode". Temps will tend to vary in the room somewhat more, but it is worth it.

As roadking advised, don't oversize!