Symetrical on both ends. Downloads from MS, VMware, etc actually get pretty damn close to that 100MBit limit.

PaloAlto PA-2000 on the head end, PA-500 on this end.

Naw, seriously, I don't expect you to solve (or even really troubleshoot) this. We've been working on this problem for months. It's just really confusing and annoying.
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I am the Doctor, and THIS... is my SPOON!