1LE springs are the same as the SS springs. Stock SS/1LE springs are:
front: 165 lbs/in
rear: 370 lbs/in
Part number comparison in this thread
http://www.camaro5.com/forums/showthread.php?t=244570
Eibach spring rates are:
front: progressive 143-222 lbs/in
rear: progressive 291-485 lbs/in
Because of the progressive design, they will deceptively “feel” softer but near the of travel, end at a higher spring rate than stock. Eibachs feels stock, if not slightly firmer while cruising but definitely feel heavier in corners. But because of the progressive design, may feel a little vague/less precise compared to straight rate springs (linear springs). Even still, Eibach would be heavier than stock and don't see why they would not work with the 1LE suspension.
1LE would actually be slightly under sprung since 1LE have better valved monotube shocks compared to 2012+ SS yet still use the same springs.
Bondurant must like the style and stance of the Eibachs because they use them in their class Camaro SS’s. People I have spoken to who have used the Camaro’s while at Bondurant had no issues with the way they feel on the track.
http://www.bondurant.com/cars/camaro-ss
Lowering the center of gravity would benefit the 1LE, keeping weight lower to the ground, even with only a 1” drop in height like the Eibach springs.