The power of the radar isn't the problem, the curvature of the earth is. If the Slava's radar is 50' high and the highest detectable point of a DDG is also 50' the radar horizon is 20 miles and the visual horizon 17.3 miles. Doubling the power of the radar won't make any difference, only raising the height of the radar will.
Here are a couple of RAN River class frigates with LW02 air search radars which will illustrate the point.
Raising the radar 10 feet gives you a mile or so extra radar horizon.nhttp://members.home.nl/7seas/radcalc.htm The Slava looks pretty high, but even if it was 70' high its only going to get you 22 miles.