An HO2 is extremely basic. An HO8 is a newer policy, but also has many restrictions and most homes don't qualify. An HO4 is a renters and an HO6 is a condo policy. There are also 3 types of dwelling fire policies. There is no HO7 that I'm aware of. In most cases the coverages available on each policy type is the same across the board, if the insurance companies base their policies on ISO standards.
OP - An HO5 is an HO3 policy but with more coverages. For example, the standard HO3 includes Coverage C on a named perils basis, but on an HO5 Coverage C is on an all risk basis. An HO3 can be endorsed (changed) to include Coverage C on an all risk basis while with an HO5 it is automatic.
Both policies will generally say that "everything" is covered except for what is specifically excluded.