Find on sorted range slower?

[Tofu Ninja via Digitalmars-d-learn]

void main()
{
        auto a = new int[100*1024*1024];
        for(int i = 0; i < 100*1024*1024; i++)
        {
                a[i] = i;
        }
        enum f = 100*1024*1000;

        StopWatch sw;
        {
                sw.start();
                auto temp = assumeSorted(a).find(f);
                sw.stop();
        }
        auto t1 = sw.peek();

        sw.reset();

        {
                sw.start();
                auto temp = a.find(f);
                sw.stop();
        }
        auto t2 = sw.peek();

        writeln("Sorted\t", t1.length);
        writeln("Regular\t", t2.length);
        writeln("Ratio\t", float(t1.length)/ float(t2.length));
}


I am getting the assumeSorted version to be about 3x slower than 
the regular find, that seems very counter intuitive. Anyone know 
why this would be, seems like a very odd thing to happen. I 
expected the assumeSorted to be faster, expect it to do a binary 
search, instead if a linear one.