For me, the HPF/D5 is not only accurate, but also the most efficient way to focus. I know some, including Jack I think, have had success using live view on the IQ back. I still struggle with live view for focusing, but I admit I haven't given it the full College Try.
If the subject is relatively close you can flip down the little corner foot on the D5, then position the D5 right on top of the camera with the foot up against the back of the camera. Makes it fairly stable without the need for mounting the D5 onto the camera. If you are really anal - sorry precise - you can add a zero adjustment to the D5 to add a small amount that accounts for the difference between wherever you set the base of the D5 and where the sensor plane is. But for my setup it is only like 0.02 feet / 0.0061m (yes, the D5 can go out 4 dec places in meters!).
I THINK the D5 is the only real effective option that works well for this application. The video feature makes all the difference.
Dave