ST3500410AS 7200.12 odd DE speed difference in explorer view

[ThomasH]

I have a 500gb 7200.12, really just started working on it, but never really seen (or noticed) this before.
2 heads. Tried both heads first, but head1 too slow to mess with so far.
Head0 copies full speed no problems, so I cloned that first completely.
Switched to Head1 only.
Head1 copies around 10sectors/second. Super slow, but getting 99.9%+ ok. Same throughout the platter everywhere.
Same forwards or backwards. (haven't messed with much else).

The odd thing, however, is that switching to explorer view in DE and copying folders/files, it copies probably 100-200x faster than when cloning 'linearly'.
Going good enough not to mess with anything yet, but what would cause such a difference?
Anyone seen this?

I don't think it's due to bad luck in the 10 or so spots I was testing linearly...as i'm pulling from the same areas with both. I think it's a setting of some kind between the 2...never really seen this before. Usually it's the other way around if there's a difference.