I haven't heard anything bad about RKSport. Of course I only hear from Camaro/Firebird and Grand Am guys, so I don't know about the Cavaliers. But everyone I talked to said they got increased performance.
1999 Chevrolet Camaro SS (PC'd)
1994 Chevrolet Beretta Z26 Q4 (W41 M90'd)
2004 Chevrolet Silverado 2500 (4WD)
My wife's cars:
1971 Dodge Charger SE (stock and original 383 auto)
2004 Subaru Impreza WRX (kid-hauler)