Well make sure that laptop A has a Full HD screen at 1920x1080 resolution. If it doesn't then you can only see anything on your screen in 720p and you wont be able to take advantege of a BluRay player. And unless you are going to be hooking the computer up to your TV at home, if you have a High Def TV at home that is, then don't get it if the laptop's screen doesn't support it.
Also, a BluRay drive is obviously going to cost you more money in the long term because you will have to buy BluRay movies. So unless you're willing to put in more money, then don't get it. A BluRay drive wont help you with DVD's and CD's.
Now will you need 8GB? Probably not. It does make your computer a bit more future proof, but the average person wont use nearly that much RAM. But is the 4GB one DDR2 or DDR3? If they are both DDR2 then you don't have to consider speed, but if you plan on upgrading A later on, you will find it VERY expensive. At least right now, a 4GB DDR2 laptop RAM module is $180, two of them puts you at $360 (to get to 8GB you will need to take out the two 2GB ones and replace them with two 4GB) or you just buy one module, and take out one 2GB and make it 6GB, but you're still down $180.
The room for a 2nd hard drive is nice, but only is certain situations. For a gamer, they would put their applications/games on one drive, and Operating System and files on another. That way system performance is optimal. But most people would only use 2 hard drive bays on a laptop for RAID 0 for super fast read/write times if RAID was supported. Some people even go for RAID 1 which keeps a constant mirror of their first drive on the second drive that way they have a complete backup just in case one drive fails (in RAID 0, if a drive fails, then all information is lost) so if you want that kind of performance, make sure it can support RAID if you want that kind of feature, otherwise 2 hard drives might not make a difference to you.
And are you sure that everything else is equal in the two? CPU the same? Same graphic's solutions? Screens? Hard drive speed? Because all of those will affect your system performance and one of those two might be better all around than the other!