Switching from 27" iMac to 15" MBP?

Hey all,

I have a 27" 3.06ghz iMac and now I need a laptop.

I'm deciding whether I should trade it for:

2.66ghz MBP 15.4"(I'm not sure if it's late 2008 or 2009)
4gb ram
9400m+9600m GT 256mb
320gb

My main uses on a computer are watching movies, photoshop (basic), word processing and browsing. Nothing like final cut.

Also, does anyone know of a website where all the generations of MBP are compared in a chart?

Should I go for the MBP? Or should I save up more money and buy the i5?
I know I don't need the extra power but value-wise?

Thanks.