Note: My response can only lend to support for you wanting to use Opteron instead of Xeon. I have no experience with Debian, so I will not comment on it.
=========
For the longest time, all of my new servers would be configured in some way using Dual Intel Xeon CPU's. The most recent of which was a dual Xeon 3.2 Ghz (64-bit).
Those days have long gone as I now choose AMD Opteron due to its sheer performance.
My latest machine, a Dual AMD Opteron 270, lays waste to that Dual Xeon I mentioned above. The dual Xeon has 4.55% disk saturation and processes about the same amount of data as this new Opteron; however, this new Opteron has about 20% disk saturation. The load is substantially less on the Opteron.
Another time I upgraded from Dual Xeon (64-bit) to Dual Opteron 250. Yet again, another amazing boost in overall performance.
In my opinion, AMD Opteron CPU's are better than Intel Xeon.