Hey Waterdog,
Short answer, YES.
I filmed an air test with my MXT Pro and uploaded a video of my results.
I have used an MXT Pro for a couple seasons now and zinc pennies show around 58-64 VDI and copper pennies around 68-78 VDI. However, the screen is usually pretty accurate and tells you either (ZINC) or (1 Cent), and most of the time found to be true with the exception of when the target is not a coin at all. REMEMBER! If you disc zinc, you will not see anything under zinc.
I posted my own testing on this, Here....http://www.youtube.com/watch?v=GxMpwkG9nZs&feature=youtu.be
Here is a site the lists the VDI's and Q&A's for the MXT.
http://nevada-outback-gems.com/MXT_files/the_mxt_faq1.htm
http://nevada-outback-gems.com/MXT_files/the_mxt_faq2.htm
And an MXT PRO field report. I reccomend the pro because you can listen to the range of tones and you can tell the difference in targets without staring at the lcd screen, a huge eye relief when the screen never sits still for you while detecting! Plus the pro has a ground grab button so you can grab the ground on the fly without stopping to re-ground balance.
http://whiteselectronics.com/info/field-reports/5530.html