If you've had experience with Sun environments, have you considered Solaris 10 x86 instead?
For serving up bits over the network Debian isn't going to get you anything extra, and they both cost the same. But instead of agonizing over the best bang-per-buck hardware RAID cards for Linux... you may get better data consistency, flexibility, and performance by just buying cheap PCI/PCIe/PCIx cards and feeding them to ZFS:
Yes, Linux supports a wider variety of IDE/SATA cards, but the Sol10 HCL gets longer every day, and there are many forums for Sol10/OpenSolaris/SolarisExpress full of people who can help you make the correct hardware choice.
I use Debian and Gentoo at home myself, but use Solaris at work, and my next fileserver will use ZFS.
Something to think about.
Happy New Year!