In PP2.0 the Limit with the bitrate on .wmv is only 10Mbits/s.
Yet most 1080i & 1080p avchd cams are around 17-18Mbit/s. I reckon 20Mbits/s should be available in Media encoder.
I haven't used CS4 yet, what is it's limit? If its still 10Mbits/s, would that be good enough for a final render in avchd? Or would it be better to go a diff codec like H.264 Blu ray? I really Like .wmv for PC Playback.
WMV and other export options are there to compress your video clips so that they can be more conveniently viewed (downloaded) or handled. The object of exporting them tp other formats is to reduce the size of the output files; rherefore you want a lower bit rate out of the export process than your AVCHD files.
You will have to experiment a little to find the lowest bit rate that gives you acceptable quality. It depends on the resolution that you select and several other factors.