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.
One main difference between the STK4048XI and the STK4050V is that the former is fully complementary while the latter is quasi-complementary and of a slightly older design (input stage and driver changes). The spec sheets show about 10x more distortion for quasi-complementary STK chips (although still quite low) than for the 'XI' versions. I believe the sonics for a full range amp are better with those STK chips ending in 'XI'; for subwoofer amplifiers, it probably doesn't matter too much which of the two you use.