Speed and more cores means absolutely noting without optimization for Cubase! Out of the box my new I-7900X was a real disappointment compared to my (still) I-4770K. In fact my 4770 was actually performing better! It took me more than month of testing and configuring to find the added value my new system could offer.
So for the answer to the initial question? Also cpu cache counts, but first go for speed and if you can spare the money get the extra cores. But as always with Cubase don’t expect wonders out of the box. Prepare to do some serious testing before you get things optimized.