It's somewhat a matter of preference and skill level.

Somewhere around 1.5:1 thrust to weight is the beginning of "3D capable" as 1:1 is capable of sustaining a hover with no pullout ability. 1.5:1 will pullout but slowly and without authority. Often at this ratio only the most experienced pilots have the comfort level to bring it down low as there's not much "extra power" to drag it out of a bad stick input.

2:1 PLUS seems to be the "prefered goal"

More is better in all situations, when tempered with wingloading... 30 oz per square inches seems to be the TOC average. But with all the superlight airframes coming out, 24-26 is realistic... So it's a trade between thrust and wingloading... and finding that happy medium will give you the best "experience" in your airframe.

Sometimes it is better to invest in CF wing/stab tubes/gear/tailwheel and lions than to buy a larger engine and become heavier nt he air. Other times it makes more sense to go the other way. It's an airframe to airframe decision process.

Otherwise if it was JUST about thrust... we'd all be putting 80cc engines on 50cc airframes...