I hated the 03.5 wing. I'm not sure what the ES model is but I got the wing off a regular protege and it bolted right on. It sits in a good position, so it does not block your sight. The body is essentially a protege w/ a body kit so they is no problem.
On a side note the dealer took 3 days to "find" my stock wing, came back to me with added scratches. Thats ok, it matches the small scratches they added to my #@#$#$ trunk. That scratch is in paint that you can see in the gap of the mazda emblem, any idea how to I can get at it to buff it out without damaging the emblem?
Regarding the downforce, the subaru guy said the wing on the sti provides something like 20lbs of downforce at highspeed. I don't remember the exact speed or weight, but it was not enough to justify the look IMO. Regualr subaru has 4 holes, the sti has eight or something.