For a Orange Black Red with 17/14/1 ratio, it increases manaleech by approximately 10.5x per usage.
For a Dual OB gem 18/14 ratio, it increases leech by ~12.95x per usage.
For the Amplifiers, to keep the pure Orange gems one grade lower, first perform a 16-combine(found also on EndGame Guide), and then perform the 64 combine until your amplifier gem is one grade lower than the trap gem.
Pure O increases approximately 7.8x per usage.
The difference between the 64 and 16 combines starts small, but by the grade 80s it's about 3x better. Even at G50 it's approximately 1.8x better.