The average damage each ability does based on your stats, including crits, DR, etc, is just a big formula, and the formula says 300+ Critical Rating is not optimal. Only about a 1% worse than optimal, but not optimal.
This is off topic but I saw you had posted a very handy graph where the extreme ends were basically what would happen if you could exchange all your power for crit and vice versa. I was wondering if you had a similar graph for power vs expertise as I'd love to see that. (Theoretical math is much more my bag than applied).