So I don't know the exact performance of the above mentioned parts, but I think you can safely assume, that all this alternatives will work.
Right now 4GB of ram is definitely enough, most games won't even use that. Of course 8GB might be a investment into the future, but I doubt you will see that much of a difference in the near future.
New Vegas should run smooth with everything maxed out I guess.
Skyrim should do so, too, as it is multiplatform, developed to run on 5-6 year old console hardware.
Crysis (1) is different, that game is really demanding on your system, but I think it should run ok (30-40 fps mostly?) on high-highest settings.
Crysis 2 again is developed for consoles with CryEngine3 as opposed to CryEngine2 and reportedly is less demanding than Crysis 1 was.
My advice would be to go for the better cpu instead of more ram, which can anyway be upgraded later.
Stronger cpu should deliver more power than 8GB of ram.
But look for the value you get for the money (i.e. price).