Generally the curve will look like this, the bigger the pig the more it will eat and the lower (or higher depending on how you look at it) the FCR gets - the bigger the pig the more you feed and get lower gain per kilo.
At one point I wanted to raise BIG finish pigs. I took a look at raising them beyond the typical 100 kg level and found the FCR "bad" (at least with my budget). The 9 baht per day gain was not worth the risk AND buyers generally started to reduce the price offering for pig over 100 kilo.
Surin Farm no longer raises finish pigs except for ones that we end up not selling for some reason. We have determined that for our farm selling piglets is what we are best at.