DO you have the top link to tight.?...... it should be fairly loose as this allows the mower to move up and down and follow the terrain, obliviously within limits. Finnish mowers will give you a lawnmower type cut......flail mowers somewhere between a finish and a bush hog, depending on the type of knives you use. for 5 Ac of grassish type lawn, the Zero turn will be the best and fastest, but you should go to a commercial heavy duty type, cause it sounds like some of your lawn is almost more pasture than lawn. Everything you want to know about Flail and finish mowers got to tractor by net .com.......there is a 600 page flail mower thread. You can search there for all three