About the thirst, also make that u can drink for the oazes and like that... and make so if u are thirsted u could see what is not happening Like fake oazes ;P
No, its not just you, i get same thing also. Paul helped me and said to get lower fps u need to write /trees low , press F8, press F12 for lower quality. 3 times(Until you will get 62m i think.) There was one more command... But i forgot ;( (stupid brains!)
------------------------------------------------------EDIT--------------------------------------------------------------------------- You can also do /flora low and /grass low