Just to give u an idea...
In the recent issue of Import Tuner they did a dyno test on a 93 integra GS (b18b1)
STOCK dyno:
118.3 HP
110.7 TQ
Dyno 2, added Greddy Ti-C cat back
121.9 HP
113.1 TQ
Dyno 3, added AEM cold air intake
123.2 HP
119.4 TQ
Dyno 4, added DC sports ceramic 4-2-1 header
127.9 HP
119.8 TQ
so In that I would say for power the best bang for the buck is the header, backed with a nice cat back
the CAI will net u much more TQ but not much HP
however something to see from the stuff above..
Total spent all all upgrades: $1,385.59
Total HP gained: 9.6
Total TQ gained: 9.1