I hadn't actually heard of Kui Buri before. I just googled it, and the photo at the top of this page is awesome! - Kui Buri National Park
My view would be to just do Kaeng Krachan because it isn't many days which you have. There are gaur there at night - ask the guide about seeing them. They visit a pool or salt-lick or something by the road in the evening but I'm not sure where (I never have a car).
With a guide you should get loads of birds
I forgot to put about Pak Thale. I visited there too (in a car with the couple who had seen the Stump-tailed Macaques). If you don't have a scope it is utterly hopeless. None of us did, and we were counting on running into other birders there, it being a Saturday. But no luck. The area is too big, too many thousands of waders, and the Spoon-billed Sandpipers too few in number (we were told there were four there...). I would still say for you to go and try, because you may be in luck and find one near the paths or meet some other birders there, but don't get your hopes up. If you do go, the pools are independant of the tides, but apparently high-tide is best because that's when the birds come to the pools the most; and mornings are apparently the best time (perhaps also when you have the most chance of seeing other birders there too).
My view would be to just do Kaeng Krachan because it isn't many days which you have. There are gaur there at night - ask the guide about seeing them. They visit a pool or salt-lick or something by the road in the evening but I'm not sure where (I never have a car).
With a guide you should get loads of birds
I forgot to put about Pak Thale. I visited there too (in a car with the couple who had seen the Stump-tailed Macaques). If you don't have a scope it is utterly hopeless. None of us did, and we were counting on running into other birders there, it being a Saturday. But no luck. The area is too big, too many thousands of waders, and the Spoon-billed Sandpipers too few in number (we were told there were four there...). I would still say for you to go and try, because you may be in luck and find one near the paths or meet some other birders there, but don't get your hopes up. If you do go, the pools are independant of the tides, but apparently high-tide is best because that's when the birds come to the pools the most; and mornings are apparently the best time (perhaps also when you have the most chance of seeing other birders there too).