Here's a thread you might want to read:
http://www.medhelp.org/posts/show/369917
It's not unreasonable to ask your partner to use Valtrex or one of the other suppressive drugs. Just tell him that you would feel comfortable if he used it, and how does he feel about it? You can share the stats with him that you put up here. What are his experiences with suppression in the past? Has he already done it for other negative partners? Is he familiar with the medications at all? These are good questions to ask him to see where he is on all of this.
You only need to wait 3-5 days for suppression to kick in. According to the doctor, the drug takes effect on day 1, but you can wait 3-5 days just to be sure.
The statistics you quoted are correct. I think you are getting at least 50% coverage with use of suppression, and I've seen all kinds of numbers ranging from 50-90%. I'd go with at least 50% decrease in transmission with suppressive medication. Add condoms to that, and your risk goes way down again. I use suppression with every negative partner I have, both with condoms and without, and I've never passed it to anybody.