The air frame manufacturer will provide you with their recommendation. Like I said, they call 'em 40 size, 60 size 120 size airframes. That means - use a 2-stroke .40 (or equivalent 4-stroke), use a 2-stroke .60, or a 2-stroke 1.20. You can usually upgrade a size but beware that the progressively bigger motors weigh more, are longer and wider, and require bigger mounts. There will come a point where a bigger motor / mount configuration just will not fit or is so friggen heavy that you'll have a real over-powered turd on your hands that won't perform anywhere near the way the designer intended.

Bottom line - you can bolt up as much HP as you want to pay for.

Oh yea - you being at sea level you can follow the manufacturer's suggested engine sizes. I'm at 5900 feet - IMUSTupgrade to come close to the "designed for" performance envelope.