Hughes,
Editing HDV natively is not a big deal, but it’s not a good idea either. FCP has to conform it to update the GOP structure. It’s a bad editing format. Change your sequence settings to ProRes or 8 bit uncompressed. Or, capture to ProRes via firewire in the first place.
I edit ProRes on a MacBook Pro all the time. Which one do you have?
Have a wonderful day.