I think you should just stick with the 410. I get wanting to downsize thinking you just don't need all that much. But I tell you this, it's always better to have too much than not enough as a bassist on a gig or at a jam. Not to say that a GK 212 wont give you a hell of a lot with your head. But the 410 is IMO one of the strongest cabs out there short of full range cabinets. I have been using a Neo 410 for over 5 years now and I am still VERY happy with it. I play in a loud rock band with 1 guitar and it is more than enough. I can't think of a time I didn't have enough volume on tap.
I've considered adding a second 410 the last year or so but I simply don't NEED it. I would really like to and hopefully will one day. But its not something I NEED. But I do get where you're coming from. But I guess like I said, I learned long ago, as a bassist, its always better to have too much than not enough when it comes to power and volume.