Well that's really not something that there is a true answer for.
I have a good attention span, so I can follow things for a pretty long time.
(So if I ever complain that a story has lost me, it is either really fucking bad, or they had non-stop speech for 10 minutes straight)
But just cause I have a good attention span doesn't mean that everyone else does; so in your game, have a replay of it, see if you can shorten the dialogue but still provide the necessary lines that you needed to give.
Colour codes work well here, but only on the actual important things.
Short and simple, you can't please everybody, if you can't find anyway to fix it, well that's too bad, it's time to get on to the next thing you were planning to do in your game.
Ugh and don't worry about recording your own voice... I know EXACTLY what you mean, mine is just terrible, even worse is that if I needed to do voice acting I would have to do the female voices as well... That would severely cripple both my voice and my male pride ;_;