Uint8Array over SPI

Hi,
while I am fiddling around with driving an epaper display with Espruino Wifi I'm still having issues with writing data. Just to be sure:

Is this:

var a=0x0;
for(let i = 0; i < _bufferSize; i++) SPI.write(a);

different from that?

var a=0x0;
SPI.write(new Uint8Array(_bufferSize).fill(a));

First one actually writes the RAM of the paper correctly and after update it will display correcty, but its slow (3.5s for 5800bytes).

Second one is fast, but seemingly doesn't update the RAM of the paper, because after update it still displays the same.

In the reference it says:

For maximum speeds, please pass either Strings or Typed Arrays as arguments.