Test kit is a good idea. Wouldn't go any lighter than the 50-55# you're thinking about. Monarch is a pretty zippy bow, particularly with a ff string. I've always found them to shoot a fairly broad range of spines well. I'm a little surprised the 60-65# don't shoot well for you. Most I've owned and seen have been cut 1/8 from center, but the leather shelf/side plate is usually rather thick. Could substitute a thinner side plate. Also, it's a good idea to check the spine of the arrows you're shooting. They're not always what folks say they are. Good luck.