was wondering what i can use to cut these guys down to size.
Take them to a pro shop. They will only charge you about $.50 per arrow to cut them. You would be real upset if you screwed up a $140 set of arrows wouldn't you?
Will the difference in the lighter arrow weight increase my speed enough to maintain the same Ke put out?
No. You will increase your speed but you will decrease the arrows kinetic energy as well as the arrows momentum.
As you decrease the weight of the arrow the bow becomes less efficient at transferring its stored energy to the arrow. Because the bow transfers less energy to the arrow the arrow stores less energy.