If all you do is go up 9w and climb Perkins than you need to try some of the other roads and hills in the area. Seven Lakes Drive, Rt 106 (though it may still be closed from last years storms), Tiorati Brook Rd, Arden Valley Rd, all wind through Harriman Park and end up crossing 7 Lakes Drive at some point. Closer to the bridge you could avoid 9w and cut down to Tenafly and pick up County Rd 501 for a flatter trip to Piermont, or better make a left off 9W at the Esplanade and explore the hills and estates at Rio Vista. The only ride in Westchester that I do regularly is the North and South County Rail Trail. You can find the start of it at Van Cortland Park in the Bronx and take it all the way to Brewster NY. You might want to check out the ride library at the New York Cycle Club (though it might be a members only section). Also check the websites for other local clubs to see what rides they might have listed.