That little 4 ton split almost everything I put on it. I mean I had 3' rounds of pine on that little thing and it split like a trooper.
There was only a couple times it would not split, and that was really super gnarly maple. Matter of fact, even my hydro didn't split it.
I am very pleased with the Ryobi, and it did much more than I thought it could.
I suggest a 12 gauge extension cord at minimal. That is what I used.
On larger, tough rounds, just chip away from the outside in and you will do fine. Unless your splitting a straight grained, easier splitting wood, like red oak, ash, cherry, even maple etc., on the larger rounds (24"+)you may have a tough time trying to split down the center in, just work your way from outside inward.