I would stay away from the solid copper... current flows more along the surface of the "wire" especially high frequencies (spark draw). With a solid bar the total surface area of the "skin-depth" is small compared to stranded wire (each strand carries the same "skin-depth" area). Full disclosure, I'm using #1 automotive wire but it's been recommended to me locally to use 2/0 welding cable for it's lower resistance and more importantly, it's flexibility makes it easier to work with. My wiring is a mess and I may go this route at the end of the season...

Two cents,

Chris