Replacing 2 Year Old Internal Hard Drive ? Options

[Milca]

I have Power MAC Dual G5 2,7 GHz which has a Western Digital caviar ( WDC - WD2500JD ) - stock drive - 250GB.
I’m adding one more internal HD which is going to be seagate Barracuda 400 or 500 GB - SATA - which I’m planning to use as an audio drive.
It’s important to note that since I’ve made some big mistakes as far as handling my apps I’m doing “ erase and install” on my boot drive Caviar and starting from the scratch - Basically doing whole new setup with my music apps,sample libraries and back up.
So my first question is whether would be wise( besides adding seagate to second slot) also to replace my two year old caviar with a new and stronger drive (since I’m doing the whole new set up ) or it is just fine to leave the caviar in there and use it probably only for my music and other application and as a boot drive.

Reason I’m asking is that I’ve read in couple of posts that I can get better performance of my boot drive with bigger drives or faster ones like raptor
Basically since I’m installing all my apps right from the start - I might as well do it on better and faster drive.
On the other I don’t want to waste money for two new internal HD if Caviar will work just fine?

I would appreciate any feedback
Thanks for your time
Milan