I had one with an OS 108 and I did not need for more power. That being said I currently have a Circus Hobbies Reed Falcon that is just a tad smaller then the DP Ultimate with a YS 140DZ and it is a ton of fun. To be perfectly honest, I think going with the OS 160 or a gas engine will make this airplane too heavy. Mine balanced perfect with the 108, with an engine too much heavier you will need to mount the elevator possibly the rudder servos in the tail. If you need to buy an engine I would highly suggest the YS 115. It is much lighter then any of the options you mention yet will spin a 16x10 at close to 8,500 rpm.