Do generic interfaces in C# prevent boxing? (.NET vs Mono performance)

public interface IMyInterface
{
    void MyMethod(object arg);
}

public class MyClass1 : IMyInterface
{
    public void MyMethod(object arg)
    {
        MyObject obj = (MyObject) arg;
        // do something with obj...
    }
}

public class MyClass2 : IMyInterface
{
    public void MyMethod(object arg)
    {
        byte[] obj = (byte[]) arg;
        // do something with obj...
    }
}

public interface IMyInterface<T>
{
    void MyMethod(T arg);
}

public class MyClass1 : IMyInterface<MyObject>
{
    public void MyMethod(MyObject arg)
    {
        // typecast no longer necessary
        //MyObject obj = (MyObject) arg;
        // do something with arg...
    }
}

public class MyClass2 : IMyInterface<byte[]>
{
    public void MyMethod(byte[] arg)
    {
        // typecast no longer necessary
        //byte[] obj = (byte[]) arg;
        // do something with arg...
    }
}

void Bla<T> (T a, T b);