Vietnam forum

I won't comment about your general plans as I haven't overlanded through Laos, etc.

But... one thing to consider is that you will be arriving in Vietnam twice (assuming you don't actually live in HCMC?), which I presume means two entry visas (at $US20-25 each). It's not necessarily a big deal in the big scheme of your plans and other expenses, but just thought I'd mention it.

If you like motorbiking the Bolaven Plateau (see http://www.travelfish.org/feature/83 and http://www.travelfish.org/feature/10) is a great week worth of travel, though you can do it in less. The only problem with doing the whole circuit would be that you have to go back to Pakse to drop off your bike.

I'd recommend stopping on the way from 4,000 islands at Champasake to spend a night or two and see Wat Phu, more because of the laid back town than the Wat - as you've already seen Angkor. Then in Pakse rent a scooter and go out to Tad Lo for 2/3 nights, use it as a base camp to explore Salavan as there is no reason to stay the night there when you're at Tad Lo. For a shorter loop to save time take the northern route out of Tad Lo and loop around to Paksong for a night stay and then work your way back to Pakse. From there catch a bus to Attepeu or direct to Vietnam - the bus to Attepeu will probably take the better part of a day. I don't know the overland to Vietnam from there but as Lizzy says you will need a second/double-entry visa to Vietnam.

So, I think you could spend easily 2/3 nights 4,000 islands, 2 nights Champasak, 3/4 nights Bolaven Plateau bike ride in Southern Laos. Not sure how that would affect your schedule, just my thoughts.