Just a bit of theory. Flasing LEDs can take several times their nominal continuous current for a long time, even permanently, provided that two conditions are met. 1) The maximum pulse current is not exceeded; 2) The duty cycle is set such that the average current over a longer period of time does not exceed the maximum continuous current. I don't know what the maximum pulse current for our LED is but it usually tends to be 10 to 20 times the maximum continuous current. If the chip allows 320 mA, then I would stick with it. The other bit is the duty cycle. At 1:1 duty cycle, you are right not to allow to stress the LED for too long. Setting it to 1:5 might allow you to breathe a bit more easily.