Thanks for the response Jax. I'm flying Bangkok Airways direct from Siem Reap to Phuket. I'll look into changing the flight but I wonder if flying out of Cambodia complicates things.

A 3 hour drive doesn't seem bad at all and Koh Lanta looks very nice. One of my reasons for heading to this area is to see and hopefully kayak Phang Nga Bay. Is that still easily accomplished from Koh Lanta?