I've made strings like this several times, and it will work. It also helps to put a smaller diameter center serving on, and then adjust your nocks to fit the new diameter (or use Magnanocks). The other thing that will help, is to make the cable a bit shorter (or twist the one you have). This will put more pre-stress on the limbs and up the poundage. Once again, not something your bow is warranteed for, but it will work. You can easily get another 4-5 lbs draw weight, if you want it. This will increase your drawlength, so make sure you're dealing with a string maker who knows what they're doing, if you don't want a longer drawlength.

By using the lighter string and shorter cable, I wouldn't be surprised if you could gain 20 fps. Of course, this may have a negative effect on arrow spine and flight characteristics. I'm not familiar with your arrow's spine range, but you may end up with a flatter arrow that doesn't fly so well.