igor, the area you are mowing per yard of forward travel is 22% greater with the 22" mower compared with an 18", and an 18" mower with 3 hp is barely adequate - and not even that for heavy grass. On top of that you normally overlap a couple of inches between cuts, so you are really comparing 20" cut with 16" cut, not 22" with 18", so you are cutting 25% more grass, not 22% more. That means the 22" mower would be slightly underpowered with 3.75 hp, and you'd be running it at maximum speed a lot of the time. If I were buying a 22" rotary mower, I'd expect to see 4.5 hp for a normal back yard, and 5 hp if the going was likely to be tough fairly frequently. That way you could run it at a sensible engine speed instead of flat out, even in six inch grass. When you get into the 18" high kikuyu, you'll still have it flat out, and won't be walking all that fast I think. (Those figures are based on what I've found with various mowers in my back yard - my 3.5 hp 18" Victa requires maximum engine speed if the grass is 6" tall, and I have to walk quite slowly. If it's more than 6" tall, I have to go back and forth two feet at a time.)
