MacBook – find information on comparing two MacBook Pro models

I'm thinking about getting a MacBook Pro, one of the 15" ones in the low end of the spectrum.

I can see two models in on-line shops that match my price range (namely, the MD318D/A and the MC723D/A). One model is 100 euros cheaper than the other, but weirdly, it seems to have the better specs: the MC723D/A comes with a 750GB hard drive as opposed to 500GB.

All the other specs seem identical, down to the size of the L6 cache, the processor, and the make and model of the graphics adapter. The only special thing the expensive one seems to have is OS X Lion instead of Snow Leopard. Can the software update account for a hundred euro's difference?

Here are the data sheets I'm comparing: MD318D, MC723D – German only, sorry, Amazon.com doesn't seem to have them.

Where can I find reliable information on each generation so I can figure out whether the price difference is justified or not, and what the extra €100 would actually get me?