Yea ! most of them are Free, They make hundreds of different versions..Some can be faster than windows, and some will not. You will just have to pick one that suits your computers specks..
Dell optiplex gx280 does not have Two cpu's, Those Only came out in workstations/Servers.
32 bit OS will only show 3.25 of ram, Anything over that you will need 64 bit OS..
It is not slow, I have one of these and you can up the ram to 8 gigs.. It is a Dual core.. I have Windows 7 on it and it runs real fast....It just come's down to how much Money you want to spend..
What about something like this ....
http://www.amazon.com/Authorized-Refurbisher-Dell-Performance-Separately/dp/B0092649HI/ref=sr_1_7?s=pc&ie=UTF8&qid=1400509357&sr=1-7
I am going to be setting a Quad Boot, And i want to use Windows 7 & Windows 8.1 and I will be using Two versions of Linux with Two Hard drives...
Which Is the best Method to do this ? Plus What boot loader/Manager to use ..