Mac Mini vs Dual G4 1.25ghz

I was looking at these two computers. I think I am going to buy a pc and mac, since I need a PC for some things. So instead of buying the single G5, i might get one of these. Now I can find them for around the same price on ebay. Which one would be better? Upgradability would be the Dual G4, but since I would already have a pc, would the mini be a better secondary computer?

Mini: takes up less space, full warranty if bought new
G4: Probably faster (dual CPUs) more upgradable (video, PCI, drives, memory)

The mini is a great secondary computer, and has the advantage to be small and silent.

Leaving the upgradability aside, the Dual 1.25GHz G4 is faster, because of the dual CPU setup, each of them having 2MB L3 cache (the mini has none), faster HD and the HD and optical drive being on separate IDE buses (the mini has both on one IDE, which makes filetransfer from CD/DVD to HD extremely slow compared to a G4 tower).
Even my single 1.25GHz G4 is faster and less laggy than my friend's 1.42GHz mini.

On the other hand, the G4 is bulky and VERY noisy (compared to the mini).

yeah the g4 is noisy, but i would still go for it. If something breaks down, it is a lot less work to fix!

I like the Dual G4. A lot of people have more than one PC as well so I don't think that matters. Having a nice PC and a nice Mac is pretty nice imo. I just could never see myself buying mini just because it is limited in upgradability. Only reason I have my iBook is for portability otherwise I wouldn't own a laptop. I like stuff I can upgrade.

But that's just my pref, if you want something small and out of the way the better option is the Mini.