I too never injected coke but GHB plus a line of coke is a great combo, in moderation of course. As with alcohol, a little coke offsets the soporific effect of the G. If GHB were easier to find I bet it would be a popular mix.
I find GHB way more fun than opiates. If I'm in discomfort, then opiates are great. But if I'm in a normal frame of mind they don't do that much for me, whereas the right dose of GHB is euphoric, sociable and energizing. And unlike opiates I don't have cravings for GHB if I take a week or a month off.
And benzos do nothing fun at all, just knock me out and make me groggy the next day.