Mandy, I just quickly skimmed over your post and the replies. I don't have a lot of time but I'll try to me as helpful as I can as fast as I can. It's almost 2300 and I need to go start supper.
I've been bowhunting for 30+ years exclusively when it comes to big game. Yes, you're right that lowing the poundage will affect the performance of a bow. Normally speaking, you better off shooting 50# peak weight on a 40-50# bow than 50# on a 50-60# bow.
That being said, with today's tremendously more effective and efficient bows, the difference is most likely so minimal as to be basically a moot point.
More important will be matching everything else up. Make sure the draw length is correct, the FOC is correct, the arrow weight is correct, the broadhead choice is correct, etc. Figure out your kinetic energy based on arrow weight and arrow velocity. There are plenty of charts that will help you with that along with recommended kinetic energy requirements for specific species. Go with a good sharp cut-on-impact broadhead (and there are plenty of 2, 3, even 4 blade models) and not a chisel point or probably open on impact type. Then stay within your maximum effective range, take only good broadside, or quartering away shots, practice, practice, practice - and you should be good to go!
Oh, almost forgot. I currently use a Hoyt Deviator that I've had for years. I shoot an XX75 2514 that is 30" long. I think it weighs just under 600 grains if I remember right. I am shooting 67 pounds and get between 247-250 fps depending on my release. I shoot fingers. I still have a Darton Lightning as well and I have it set up to shoot the same - just different arrows length and poundage but same weight and speed. I got the Deviator about 3-4 years after they came out off of
eBay at a fraction of the cost of what they sold for brand new. Needless to say I am quite happy with my
eBay purchase.
Hope that helps.
God Bless,