I just got back from a quick day trip and found lens juggling between my primes to be a PITA. I currently have the 8mm f/1.8 FE, 12mm f/2, 17mm f/2.8 (an exceptionally sharp copy) and the 75mm f/1.8 lenses. I prefer the primes for street shooting, but not so much for vacation snaps. I've been debating picking up the 12-100 f/4 Pro, but for about the same price or even cheaper I can find a new or clean used 40-150mm f/2.8 Pro. With the 8mm f/1.8 and 40-150mm f/2.8 lenses I can cover the extreme FLs and the 40-150mm can double as a portrait lens, though I'd still have the dilemma of lens swapping. If I go for the 12-100mm f/4, I'm wondering if I'm already covered with the 12mm f/2 and 75mm 1.8 which are both significantly sharper and faster. I still like the 17mm f/2.8, because I have a killer copy of the lens and it makes a nice one lens solution for street shooting especially since it's a pancake. My other option is save some cash and get the 14-150mm II for those family snaps. Brand new grey market copies are selling for $299 on ebay right now from The Games Arena. I tried a copy in-store that seemed quite sharp, but I'm not sure if I'd be happy with build quality of the lens since it seems to be quite plasticky. What do you guys think? Thanks for any opinions!