A 4-4?
There's 8-in-the-box with a hard hitting SS coming closer to the line. But a 4th 'backer? That spells trouble. Smart teams and savvy QBs will just go over the top and destroy you with the pass. An extra blocker, shotgun formations, these would be utilized to counter this. The front seven has never been a front eight because it would upset the balance of being able to equally defend both the run and pass.
With a 4-4 you might be un-run-on-able, but teams would unleash an arial assault on you that would god damn embarass you.