RE: Smallest sail on a carve 162
I think that you will be fine with the 7.0.
If you use the 5.7 you might want to try a smaller fin and moving the footstraps more towards the center. That could make it more comfortable.
Since you are pretty heavy, you should be able to use the 162 in stronger winds and with smaller sails than would be comfortable for a light guy. It's worth a try anyway.