Going to build a Freenas box for storage only(local, no ftp etc)

I was going to get 4 of these:

http://www.oczone.co.nz/product_info.php?products_id=33379

With 500gb Hdd's mirrored for safety. All connected to one of these:

http://tinyurl.com/yl372xj

The system will be an old socket 478 board with an Intel pentium 4 1.7ghz, along with 512mb ram and a TP-Link TG- 3269 Gigabit network card(I'd like to make use of my gigabit siwtch).

Has anyone ever used freenas with this sort of hardware?

The only problem i've faced with freenas in the past is rubbish gigabit speeds(may look into openfiler too)

Cheers :-)