Well one thing to consider about a 4-3 is that when you go into a passing defense with nickel/dime unless you have pass rushing LBs that you can substitute to play DEs in those packages you are probably left with a mediocre pass rush because you will have two big run stopping DEs and two NT types at DT in your 4 man front. Granted some defenses have their nickel be a 2-4-5 deal that keeps all the LBs in for the pass rush. So that may be something to consider.
Also a 4-2-5/nickel can be very similar to a 4-3 depending on the capabilities of your 5th defensive back (this is one area I wish that the depth chart allowed for a nickel back position).
I actually believe USC went with a 4-2-5 as their base defense last year to get another safety type of player on the field to have more speed in the defense to help defend against Oregon (and you may have seen how that turned out...).
Edit: on the subject of extra spaces on the depth chart I wish we got the following splits:
Outside, slot WR
Boundary, field and nickel CB
SDE instead of LDE (SLB and LOLB as well)
WDE instead of RDE (WLB and ROLB as well)
DT and NT separated