The 6.2L and 6.5L are nearly the same engine, and share a lot of the same parts. The 6.5L evolved from the 6.2L, so it is a little better. Comparing a 6.2L n/a and a 6.5L n/a, the 6.5L will have more power, just because it has more cubic inches. Plus, the later designed heads and exhaust manifolds and fuel injection system give it a bit better performance. Both will work fine.
Casey