These threads will be of use to you.
Q1. That is outdated information. Cubase utilises multicore.
Q2. SSD’s will see you HUGE improvements.
My new build…
Browsing Sample based Synths presets is a dream, lightning fast load times.
Rendering, bouncing samples, offline processing etc… unbelievable speeds.
The i7 will clock as fast as the i9. If you want to maintain turbo/OC for long durations, the new bottle neck is the quality of VRMs and it’s cooling… You’d need insanely large projects to eat up all that ASIO, even at tight latency, which if you did, only the highest spec motherboard would maintain. Meaning the price jump isn’t just in i7-i9, it’s also in MB. The i9 will run fine on the cheaper z390’s but it’s extra capabilities (which you won’t need) won’t be achievable for long.
Spending on SSD’s, especially NVMe is a much better investment.