I'd leave the cubes as is. Cubes aren't going to limit you. After you build a forged bottom, you can spin the TVS up to its practical limits anyway. About the only thing more cubes will give you is more power down low. I'm guessing with a forged bottom and 3" blower pulley, you'll have all you can handle. You'll keep a few more bucks in the bank and get a little better mpg too. You're about at the point where a little more costs a lot more. Yes, absolutely, you can push it. For me, it wouldn't be worth it. Guess you have to decide
If you are hell bent on stroking it, my vote would go for the 416. Those extra few cubes come at a price.