Hi,
I would not recommend a person buy the V3i as a nugget detector as it has way more features and a higher cost that you need just for nugget detecting. The MXT would be a better choice. But if you already own one, it can indeed find gold nuggets. I have seen it used two years in a row at Ganes Creek, Alaska with very good results by a veteran nugget hunter. http://whiteselectronics.com/component/story/title/gainesgold.html There are quite a few others who have made finds with the V3i on the Internet that can be seen with a bit of Googling.
I have to admit that I have not attempted down and dirty nugget detecting with the V3i in highly mineralized ground versus various other detectors so I can't answer the question directly from personal experience. If the V3i had glaringly obvious better performance as a nugget detector in the field prospectors would be migrating to it in droves and the fact they are not is telling. I have one and have to admit to not being inclined towards beating up a $1500 detector when one costing half as much will do the trick. Practicality does matter. Still, after seeing my friends results the last couple seasons I may give it a go next summer to learn more about its capability.
I did make a post early on about the obvious capability of the original Vision on small gold in air tests at http://www.findmall.com/read.php?66,928128
Steve Herschbach