Well I flew my Kingcat with a 120, 160, and a P200. All flew well. I really think the Bobcat is a bit overpowered with a p120, but I dont see any advantage to using a P70 since the weight isnt significant. The P60 looked great on this airplane, but be ready to be in the full power alot and would this be hard on the engine? I also flew the Bobcat with a Titan. Not fun. All the power is in the top end so your either cruisn or hallin ballz. I noticed the P80 are on sale. The are supposed to be 19lbs now. Probably best suited size engine. cheaper than P70, only .3 lbs heavier.
I would say P60, P70, P80 or turned down P120. If your going to be hanging stuff from the bottom and smoke, then go with P80 or P120.
The Bobcat is super strong, I believe the best arf ever.
Scott