if my car only runs good with octane booster, does it give me an idea of rwhp limit

[master blaster]

I bought the car as is, with all mods. the owner told me he had the rwhp at 542 and 531rwtq..but reduced it because it was too much for street tires to 501/499. the car only runs good with octane booster,much much better! does this imply that the tune is at its limits becuase it get kr. and its doubtfull to get more power?