OK, managed to answer my own question with a little more research... so here is an answer for anyone else searching...http://bolaven.com/bus_vietnam.php
From the renewed southern busstation at km 8 departs every day buses to Vietnam. Buy your bus ticket at the busstation.The times are only an indication!! and are exact as published at the busstation.
There is a rough timetable and prices on the website.
Does anyone have any experience of doing a Pakse to Vietnam trip?
#2 Jimbobber has been a member since 18/11/2010. Posts: 11
It doesn't seem so far on the map (relatively speaking, compared to the Pakse - Vientaine trip which gets OK reviews) - is the road worse?
the timetable suggests 6.30pm leave Pakse, 10am arrive Hue. Add another 12 hours for Hanoi!
I guess I will have to grin and bear it as I don't have the cash to fly!
#4 Jimbobber has been a member since 18/11/2010. Posts: 11
We travelled 4,000 islands to Hue and on to Hanoi last January and it was painful indeed. It entailed a boat from the island, a big bus to Pakse, some confusion about which bus station to take us to, a tuk tuk ride to the Northern bus station, a 4+ hour wait (whilst looking at the tiny, crammed, uncomfortable minibus that was to be our onward transport - despite the fact that the person we'd booked with said it was a big bus) and a very uncomfortable and frequently scary ride to the border. A 3 hour wait at the border and then a few hours drive in Vietnam. We then waited for about 6 hours and took the overnight train to Hanoi.
But having said all that, I don't regret it and now it's just 48 hours of my life that I look back on and laugh about. Ha ha ha.
By the way - you mention the Southern Bus Station. I'd looked here in advance of going to 4,000 islands and they certainly listed buses to Hue. We argued the toss when we were dumped at the Northern station (I called the guy who'd sold us the ticket) but was firmly told that they left from the Northern station. So it might be that you will get ferried from the South to the North station if you buy direct.