Just to be back on topic ;), C7.5 works very well here. I realise, in comparison to many others here, I don't use large numbers (4-7 Omni, Kontakt, Trilian, Massive etc.) of VSTis but do use a lot of hungry VSTeffects, including 2 or 3 instances of Nebula with rather heavy presets. UAD plugs are a huge help.
I've learned to work with my aging machine, and what's funny, I don't feel like I'm missing anything :).
One thing about aging machines (not me!), you get to know them really well, and that makes for a stable system. It's a shame upgrading seems to become necessary sooner or later.
But...different strokes for different folks,
I started using an EFI based motherboard about 6 months ago, with a 4K sector drive and the benefits cannot be understated.
Secure fast booting and large file access with more efficient storage are but some of the benefits of upgrading to a new machine.
No point being a luddite when it comes to Cubase!