The 980Ti (reference and AIB) will generally OC to 1450-1500ish. The issue is keeping those clocks, while it may seem logical that AIB custom cooled version will hold OCs longer this is not my experience. My 980Ti EVGA SC+ ACX will happily OC to 1450 but will drop to mid 1300s after 15-20 minutes in W3. The AIBs dump air into the case and this does not help keeping the GPU cool.
I only managed to eliminate this core clock dropping by adding AIO WC Accellero Xtreme Hybrid. This kept the core clock at 1430-1450 OC.
Obviously the 980Ti is an excellent overclockers compared to AMD Fury X, AKA "overclockers dream" (still makes me laugh). Though it must be considered that base boost clocks on even reference 980Ti cards are generally 1270-1300 or so. They just don't stay there long, though most reviews cottoned on to this Nvidia unsustainable speed boost that only lasted 10-15 minutes at best.
So in general most review sites will run their cards for a heat up period. When they do the 980Ti is still overall a superior card to an R9 Fury X. The Fury X is still an excellent GPU, just overpriced compared to 980Ti IMHO.