convert -density 400 somepdf.pdf -scale 2000x1000 output.jpg
The key is the "-density 400" switch and also -scale 2000x1000
To give credit I found the solution here: http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=10928
That was the perfect solution when I was frustrated with how small the resulting JPG's resulted. I'm sure this will help a lot of people when it comes time to converting a PDF to JPG which I'm amazed Imag........