Which HD format for editing 720p on white iMac?

[derekjd]

Quick question for you video gurus. When I'm converting h.264 720p content from my cam to edit, whats the lightest to convert to? I've been using Apple XDCAM EX 720p30 (35 Mb/s VBR) and it seems it's a little to much for my system (White iMac C2D 2.16 w/ 3 gig). When using FCE my system will consistently choke while playing back added effects and in turn I need to burn time to render. Would Apple HDV 720p30 or Apple Motion JPEG A be per say lighter and easier on the system to work with? How much video degradation will I notice?

Thanks in advance.
Derek JD

 

[DPA]

I use apple prores 422 when capturing HDV. By lightest do you mean lowest file size, highest quality, highest hue, etc.?