how hard or how much pressure you put on the wheel will dictate if it bogs down, you can bog any size motor down and it will result in overheating and failure. So you can also successfully grind something with a smaller motor it will just take longer because you cant push as hard against it before it bogs. I would go with the higher horse motor because it wont heat up as much if in fact you do put to much strain on it and your sanding , grinding will go much faster as a result.
https://www.thefabricator.com/stampingjournal/article/cuttingweldprep/four-factors-to-consider-when-purchasing-a-grinder--you-get-what-you-pay-for