I also edited this piece of code (still in si_dpm.c) to let my memory clock hit
1400 MHz which is stock speed for this card, and I'm still running rock solid:

    /* limit all SI kickers */
    if (rdev->family == CHIP_PITCAIRN) {
        if ((rdev->pdev->revision == 0x81) ||
            (rdev->pdev->device == 0x6810) ||
            (rdev->pdev->device == 0x6811) ||
            (rdev->pdev->device == 0x6816) ||
            (rdev->pdev->device == 0x6817) ||
            (rdev->pdev->device == 0x6806))
            max_mclk = 145000;
    } else if (rdev->family == CHIP_VERDE) {
...

Not sure why it doesn't hit my 1450MHz overclock (which is flashed to the
card's bios), but I'm very pleased compared to the previous 1200MHz.