dimension for high quality FLV

[yunakokimama]

I convert H264 HDV 1080i video ( I use Canon HV30camcorder) to FLV using adobe flash CS3.
I set dimention 1280(height) 720(width) with high quality setting
.
File size is 155 MB. I think this is not too big, but when I play the video on my mac computer, it is jumpy, not smooth.
Should I setup dimention 640(height) 360(width) for smooth playback??
But size is the same with the both video.......