it looks like this will do both sending and receiving. Bit of a shame it overwrites the transmit buffer to do it tho
Yes, it does, and it is 
It seems that it would be nice if the SPI library had more features.
I've been trying to get some "bare" SPI code to work, so I can figure out whether this is inherent slowness, or some hardware/configuration issue. But I'm having troubles getting it to work
Ahh, there is goes... This code produces a nice tight loop, and I'd really expect it to keep that SPI clock going pretty much continuously. It doesn't Therefore, something "interesting" is happening! (I had to modify SPI.h to make SPI.spi a publicly accessible value, but otherwise it has no modifications.)
#include <SPI.h>
Spi *myspi;
void setup()
{
SPI.begin();
Serial.begin(115200);
myspi = SPI.spi;
}
void loop() {
Serial.println("Begin bare metal SPI test");
SPI.beginTransaction(SPISettings(28000000, MSBFIRST, SPI_MODE0));
for (byte i = 0; i < 100; i++) {
while ((myspi->SPI_SR & SPI_SR_TDRE) == 0)
; // spin
myspi->SPI_TDR = SPI_PCS(3) | i;
}
SPI.endTransaction();
Serial.println("Bare metal finished");
delay(1000);
}