I trust Derek!
And for me I can say, my C5 was not bad for calibrating Grayscale & Gamut.
But my experiences are, it was better to calibrate my Mitsu HC5000 in direct mode reading (faced to projector), cause the bulb wasn't any of the brightest. This has 2 benefits: 1. I can read 10 IRE without problems, 2. readings are faster cause the meter gets more light.
And to get a more correct D65 calibration in direct mode, I also dertermined the (little) screen offset by performing first a reflective and afterwards the direct mode reading (same IRE). As delta I got the screen offset x=0.0038/y=0.0104; as you can see, very low and not really significant for D65.