Serygo said:I am wanting a pretty big tank after I get a job or something...
1500g tank hopefully10' x 5' x 4'.
Um, that's still too small. A tank with a 4' side won't give it enough room to turn around after 6 months. Not to mention when it hits the 10' or larger mark. If you start messing with growth rate, all you are doing is providing improper care for a fish that requires ALOT of knowledge before attempting to own one.
Just the food budget alone is more than 98% of the fish keepers can afford.
To answer your question, a properly cared for gigas will grow in front of your eyes. The two I'm running right now have grown 4" in the last 6 weeks. They also bulk up quickly as well, not just length.