Your cpu should work fine! You can test this with dawbench (google). If with dawbench you can load your cpu into the 80% with a 128 buffer(I can up to 95% with RME PCI card, but usb is a little lower) Cubase and your cpu are fine. Then it is either a plugin (brand) or the structure of your projects that cause this (busses with heavy processing can cause this for example)
which plugin or bus is easy to find by disabling (turning off, not bypassing) plugins until you find one that drops asio load significantly. Also some plugins have extra high loads at (very) small buffers. Performance wise 256 is ideal.But I run at 64 or 128 mostly and I have an even older q9550 4 core2quad. If your motherboard has overclocking capabilities that will help a lot too. I run my 2.83ghz @4ghz.
Cheers!