1) The RAM isn't the fastest, but 1600MHz CL8 is very fast RAM, getting faster RAM will only provide a tiny performance boost, for a large cost boost.
2) Personally, I would use the extra money to put towards the monitor fund. I would suggest
this lovely 22in e-IPS panel monitor (
here is a review). The difference over TN really is spectacular.
3) In games the i5 is just as fast or a bit faster than the Phenom II (
here is a review). Considering the Phenom is running a 3.4GHz and the i5 is running at 2.66GHz, this is pretty impressive. Also, bear in mind that when overclocking both chips top out at around 4GHz, so a fully overclocked i5 is much faster than a fully overclocked X4.
With this all said, from a budget stand point the Phenom II is more than fast enough for modern games and costs a bit less. If you don't plan to overclock then it is a very good choice.