i have the z920 with 26hp kawi. in normal conditions it did fine with stock blades. it would bog down in heavy growth and wet conditions. i would have to slow down a good bit in those conditions. then i started using the oregon G6 blades. i guess because of the slots in the blade there is less drag. ever since i did that the mower no longer bogs down no matter what the conditions. you will also want to get the suspension seat. i got that and it made a huge difference in the comfort level. after mowing 2hrs without the suspension your back would start to feel it but now with it i can mow all day and not feel a thing.