For fun I ran NUGT on the high perf KISS, here are those results and I also added the GDX KISS for comparison:

First off on NUGT - it's a 2X ETF and degrades badly, you can see this from the NUGT buy and hold, just a disater and these leveraged ETF's are not meant to be held long term, they are trading instruments and this demonstrates that, and look at those yearly draw downs of 73%, and 90%!

But KISS manages to produce VERY nice gains, man especially that 2016 year, it made 517%!! Jeez

Obviously you can just just double up your GDX position size, however I'll probably trade both because once in a while GDX is better (2018) and other times NUGT is far far higher.