I've never had a Sonar project that uses more than 2GB of RAM, but I do stay away from huge sample libraries. I do use BFD, Addictive Drums, Garritan Personal Orchestra etc. etc. Mind you, I'm doing tunes with 80 plus tracks, full live drums, percussion, many keys etc. etc.
Also keep in mind that in some form factors i7s are barely any faster than i5s because you run into the thermal dissipation limit with either when pushing hard. Finally, an 8th generation i5 is faster than a 7th generation i7 in the same TDP.
TL/DR: 12GB is MORE than enough, spend your money somewhere else...