Hello Zulkarnain,
It is a good question. Here I agree with atul to some extent. If you consider any system the efficiency and gain are related and both do have a trade-off with the performance. For achieving high efficiency , we require high gain and theoretically the higher the gain , more efficient will be the system but practically with increasing gain to some level , the non-linearities cope in. I hope you understand the relation. Hope it helps you.
Regards