Lag during multiclip...why?

I've been spending weeks trying to figure out the perfect workflow for my gear / editing system. This is my last step. Putting two clips shot from two different cameras into a multi clip sequence to edit. Once i create the multi clip it seems to play for about 5 sec before stopping completely. This worked before and i don't understand why it's not now.

I used to work with HDV footage but after researching and reading i saw that it's best to work with apple pro ress while editing. So i have about 400 gig of footage i just converted all to apple pro ress and now i'm having lagging issues.

Would this be the footage or my machine?

Whats the deal with online or offline . proxy pro ress? not to sure what's next.

Any ideas?

interesting. You said "storage" so i thought what would happen if i took the same two files and transferred them from my external hard drive to my HD and then ran the same test and it worked. So this would conclude that my external hard drive isn't fast enough to handle this function.

Now what? Should i move the footage to my computers hard drive or purchase a faster external? right now I'm running a 500gb segate portable drive that i picked up from staples. Is there a better known to be faster drive?

Thanks for the help!

Yes, it's connected via usb. This is how i've always done it before but that was before all my footage was in apples pro ress. I'm guessing since im working with much bigger files i will either have to get a faster external firewire hard drive or put the footage on my mac HD.

I'm using a 2009 MBP with 4 gig of ram running final cut pro 7 and Lion OS
my external harddrive is a seagate 500GB
i have a cannon 60d camera
A Sony Fx-7

My firwire port i have in the computer is a small box looking slot? is that 800 or 400?

Need anymore info?

WRP

I've converted all the footage to apple pro ress 1440x1080 to match the size of my hdv footage from the sony.

I am currently editing off of an external drive (thinking this is where the problem is, thinking a firewire 800 drive will solve this issue of lag.

Timeling setting is: safe
Playback quality: Dynamic
Harddrive speed: it's a travel size i believe the RPM's is 5400
USB2.0

Not sure how to work the online / offline issue.

My timeline is also set to apple pro ress 1440x1080.