I don't see a problem with the 10 days, if you can get the bikes. Riding at a reasonable rate its usually;
Vientiane to Viang Vieng Day 1
VV to Luang Prabang Day 2
LPB to Oudomxay Day 3
Oudamxay to Luang Nham Tha Day 4
LNT to Huay Xai or Chiang Khong Day 5
Chiang Khong to Chiang Mai,
This still gives you some extra days to sightsee.
It is also possible if you really push to go Vientiante to Luang Pragang without a stop at Vieng Vieng.
Also Luang Prabang to Luang Namtha without a stop at Ouodomxay is not too hard.
But you should stop and smell the roses, and enjoy your time. I think 10 days riding time is very doable with the new roads.
