I don't know anything about those black boxes...
It is better to remove weight from the front than the rear for weight transfer/distribution issues. That being said, weight is the enemy of everything performance oriented. Stopping, turning and accelerating all happen better with less weight. In basic terms, your trap speed at the drag strip is a reflection of your power to weight ratio. Less weight is like adding power when it comes to racing.
If you haven't already done so, I recommend relocating the 35lb battery from the front corner of the car to the right rear corner of your trunk. This won't reduce weight, but it is a good move to improve the weight distribution.
The one place that a lot of guys (myself included) tend to ignore on weight reduction is sitting in the driver's seat. I could drop 20lbs and both me and the car would be quicker