I realize this is probably not the most scientific approach, but I just played an IRL solo game with Gear as the only Kingdom card. Opened Gear/Gear, and otherwise played BM-ish. I bought Provinces on turns 5, 11, 12, 14, and 15, which puts it on par with DoubleJack. If I'd gotten a Gold on turn 5, things may have come around earlier, but I'm not sure. Gear allows a lot of leeway in terms of adding green; it draws, it can save excess money for next turn, and it can hide away Victory cards during a reshuffle.