I say all lambskin all the time. It's what was used in the first three movies and drapes wonderfully. Also, I live in CA, aka the fire pit of he**, so a warm jacket is never, EVER necessary. Not to say the lambskin isn't warm, it's just thinner. It also distresses really nicely with wear. I don't really have words to describe the change over the first year I owned it.
As for the differences between the Raiders and the LC, here goes nothing:
The jacket was originally made by Peter Botwright, now of Wested Leather, but a different company/person made the jacket for Temple of Doom. It's my understanding that the LC jacket was made based on the ToD jacket, which wasn't exactly the same as the original. After LC, Wested saw the market in selling the jackets to the public, so they started selling Indy jackets made from the new LC pattern. It wasn't until a few years ago that they actually made a somewhat more accurate Raiders jacket, and then finally the special offer jacket, which in my opinion is close enough to perfect.
The differences between the jackets sold by Wested now are the collar and the storm flap snaps. The collar points on the LC are considerably longer than the Raiders and the storm flap had a snap added at the top and the bottom. Both of these details were supposedly added to stop them from flapping around in the motorcycle chase scene. There may also be slightly larger pockets on the LC jacket to accommodate the Grail diary. I'm not absolutely certain if all those details are included or standard on the current jackets, and some of the back story may have been disproven. I haven't peaked my head into the jacket section at COW in a while since it became a war zone.