Replying to New Laptop for Editing - Need input!

Before this turns into a massive mac vs. Pc battle thread, I would like to say that I'm buying a PC, so please don't say mac. I understand macs are good for editing, but I simply do not want one.

Ok so moving on. For editing I use Sony Vegas Pro 9, and usually edit AVCHD, so obviously I need a pretty fast computer. I'm picking up the new laptop tomorrow because after tomorrow ill be on vacation and I want to bring it with me. Basically id like some input from other people who do the same kind of thing. I use vegas for editing, often use photoshop cs4, and some other big programs. Right now I'm planning on getting a Sony Vaio F series. The one I'm looking at has 4 gb ram, 500gb hard drive, and an i7 intel processor I believe.its also about a 17 inch screen. Does anyone know whether I should upgrade to 6gb ram or what? I definitely do a lot of multi tasking and need speed and power. So if anyone can give me any suggestions (preferably sony because I'm going to a sony store) on anything else in the $1000 to $1400 that would be great, or even suggestions on external monitors and hard drives. Thanks guys.