Well, manufacturers always push to provide more performance with the same—or even less—power consumption. So I think if you get a good PSU, upgrading it won't be a concern. Unless you change the equation significantly by adding another video card, place 4 more hard disks into your system, etc. In any case, PSUs are relatively cheap, so upgrading to a more powerful PSU will be cheaper in the long run than paying a higher electric bill for a PSU that unnecessarily consumes more power.
Regarding the BFGs, just saw someone in another thread recommending the LS over the GS series. I wouldn't know why though.