On what are you Previewing the final?
I've got a 512kbps WMV9 render that is 5 minutes long and is 19mb. OK, it IS for a small format,

but I think it's quality works fine. Colours are good too! just how BIG is the thing going to be played at?
You might want to try encoding in Windows Encoder. It is a free piece of MS software and makes for an amazing encode. WEnc ain't the easiest of encs to get your head around - try using 16:9! - but once you've done it a couple of times you may just prefer it..
Any reason WHY WMV? Have you tried the SONY or MainConcept MP4 options?
G