16x4W is a little heavy for the 91, I thought. Even a 4-stroke Saito 100 experiences some spool-up delay with it. Since 2-stroke mid range torque is not that strong, hovering at midrange with a large heavy prop can be frustrating. Try the 15x4W if you stay with the Webra 91. You'll get much more power, and some more thrust because it will get you into the engine's power range.

The new Webra 120 is pumped, and should give you enough power. Looks like you can't get away from adding a few more onces to your current setup.