2008 Imac vs 2011 macbook pro

Need someone more informed on these things then me to help out.

I currently use a 24 inch Imac 2.8Ghz 4 Gig Ram Intel 2 core duo 1tb - I mainly use it for Final cut basic editing - any hardcore graphics intensive after effects is done someplace else.

This machine is my first love its brilliant and has served me well BUT I'm thinking of getting something a little more portable - Macbook Pro

So my question is, If I were to but a 2nd hand (I.e - more in my budget) 1-2 year old Macbook pro will it stand up against my imac in terms of performance?

Ideally I'd like a machine that will perfom as well and which I could pick up at a moments notice while on the fly.

My early 2011 i5 MBP is a significant step up in performance from the Core 2 Duo iMac. (The i7 is better than i5, but it's nowhere near as big a difference as going from the Duo to the i5 when running FCP7).

The other thing to bear in mind with editing is that screen size is an issue - I wouldn't advise anything less than the 17" screen model unless you're going to plug up a second screen as a matter of course, which rather negates the portability aspect of using a MBP.