Do you make the test for 300w/4ohm long term runing ?
I have 8 pieces STK4050V and if it is so good I think it worth to make a multi-channel amp .
I will make the power supply for +/- 58V for 200w/4ohm with 0.1% THD ( I hope ) and I presume more safe .
If you have more details about your project, please, post more details.
Best regards!