I was there in January. We spent a week in Tonsai, Thailand (not long enough) followed by three weeks in Vietnam (too long).
If you really want I could give you the run down how to get around however I really wouldn't recommend going there if you are planning a climbing trip. It is not awesome. It is barely OK. You can order a guide book from Asia Outdoors online (They were called Slow Pony but changed their name) and see for yourself. There's about 20 climbs in Butterfly Valley on Cat Ba Island, five on Tiger Beach, five across the water from Tiger and the rest is deep water soloing (DWS).
The DWS may be good but it was too cold in January and you are swimming in some pretty manky/polluted water.
The other problem is you can't get on the climbs without getting fleeced by Asia Outdoors. Most of them are boat access only and they're the only guides who know how to get on them. Everything else is cheap except the climbing.
Even Butterfly Valley is on private property where the hand is out for dough to get on the wall.
I'd head back to Tonsai/Railay in a heart beat. Now that place is awesome.