I have a bow that I bought with 55# and 45# limbs and find that to be a good combination for what I use that bow to do. I might rather have gone the other direction if I were using the bow for other purposes. Ordinarily, it is better to buy two bows than to buy a riser with two sets of limbs. The exception is Morrison, ACS, ILF or some other bow where the limbs are readily interchangeable with different risers so you can actually sell the limbs separately. Otherwise, you may end up practically giving the limbs away.
Allan