You can gain approximatly 1 foot per second per every 3 grains in arrow weight you drop. So you should gain close to 7 or 8 feet per second dropping down to a 75grain head. There are all kinds of options to gain speed, loosing rubber tube on peep sight, taking off any none needed things on your string that add weight, shooting smaller lighter vanes to reduce arrow weight, increase draw weight, lots of little things like that.