All rearward swept wings suffer a loss of lift to some degree because
of span-wise flow. Hence wing fences on some. Forward swept wings do
not, for obvious reasons. Forward swept wings do suffer a weight
penalty because the bending moments are self-generating - any twist
results in a force tending to increase that twist, thus they must be
considerably stronger than the alternative. IMHO aircraft designed for
lower G limits would profit efficiency-wise from forward sweep.