If I use 4lb of honey for a sweet mead it is normally SG 1.125. I know Young's Dessert / High alcohol yeast has a tolerance of about 14% ABV, which normally leaves it sweet. My advice is to find a yeast you like, find it's tolerance and plan your mead from there.
My logic is that there is 350g of sugars per 1lb of your average honey. 4lb of honey is about 1400g of sugars which would give you a finished mead of 16.3% ABV. The yeast I use has a tolerance of 14% ABV, so in theory, you are left with 180g of sugar, so the end SG should be 1.020 which is a medium to sweet mead.