Go for the YS110 with 25% nitro, it will turn a 16x6 at 10,500 RPM (without muffler). Mine was turning about 9,750 RPM with the muffler and it would haul my F90 with ease. An 8 lbs plane will be a blast.

Some people find that they need gobs of power others do not. If its an 8 lbs plane and you want to just fly aerobatics then a SA100 will suffice, if you wanna 3D the YS110 will be great fun. For a 'cheap' motor the OS91FX will be good to go with, you can run it on 15% nitro. Its a very reliable engine.

Also, 200g is about 7 oz-8 oz. To be honest it all depends on what you want. Some planes are built too light or too heave that it ends up tail heavy. In that case the OS120 will be a better choice. If its well built why not go with a SA100? Keep the wing loading light ... so it all depends on what you want.