With only two bits per gun color you simply get 64 colors total. The four color base palette won't improve this much (if any). Therefore HAM4 is almost useless. Lores HAM6 will most certainly look better than HAM4 for colorful images, and hires lace 16 color with palette slicing will also look much better, and also works straight out of the box.
Then there's lores HAM6 sliced palette, and this is truly superior to Hires HAM4, even if the resolution is lower.
The best way to get many colors in hires is to use a 16 color screen and use palette slicing: You can use Floyd Steinberg dithering effectively, you can change 15 colors in the border without overscan, and you can get 12 more colors by placing sprites behind the bitmap (give bitmap pixels color 0 and the sprites will show through). Best of all, it's all done in software.
