Settings for exporting from FCP to .flv

I am producing web videos and exporting my files from FCPro 6.0.3 - I am using Quicktime Conversion - Macromedia Flash Video (FLV) - does anyone out there have a good set of setting for the best possible web quality for me?? I have been using:
Video Codec: Sorenson Spark
Frame Rate: 30
Key Frame Interval: 30
Quality: High / 700 kilobits
Maintain Aspect ratiom
Audio at 128 kbps
Size 640x480