Chrony it first. 2 of the last KA's that I've seen came out at 351fps w/0.20's with the hopup off. The one before that was 330fps...I added a tightbore, better spring guide, air-seal nozzle and it's bang on 350fps with the stock spring. With a M110 spring it's bang on 390-ish.
That's just about as close as you can get but still be under the generally accepted indoor/cqb 350FPS Maximum Limit.
If you're shooting 330fps the range/distance that you'll pick up by adding 19fps will be minimal. 10-20 feet is the matter of 3-6 big steps...
If you're shooting 300...the 35-49 fps that you'll pickup with a stiffer spring is noticeable. The difference between 330-ish and 380-ish when outdoors is noticeable.