Keep an eye on temps then, if voltage is on auto then it will probably have increased, use realtemp or coretemp to monitor it at idle and load, as for ram as mentioned you probably will see a minimal performance increase adding another 4Gb.
I would always go fresh install myself, a clean start is always good and can provide a little performance boost in itself.
windows updates don't take too long as long as you have a reasonable internet connection. You'll probably have a couple of large rounds of updates if you have Windows 7 SP1 install media. If you only have Windows 7 media then I'd have a look into a standalone SP1 installer