It looks like the Su-35 would be a step up from the F-16s Turkey's AF currently operates. But depending on the avionics suite, it might be approximately equivalent in capability and performance to current USAF F-15s. And that's assuming Russia doesn't sell Turkey a dumbed-down export version instead of the Su-35S it operates. Were I the Russians, I'd be a bit nervous selling the current top-of-the-line fighter, fully configured. The opportunities for the US to learn more than Russia might like would be pretty significant.