I have a set of 220cc brodix 11-x heads that have $1500 in porting in them on top of the initial $1200 for the heads. The heads were professionally ported and polished by HVH. They sent a copy of the final flow figures and I compared them to a set of race ready AFR 220's. At .200-.500 lift, the brodix heads outflow the 70% CNC ported heads by about 10 cfm. Above that the two heads flow the same. I dont think that would equate to a very big difference at the track. I would guess that your heads flow somewhat like the unported 11x heads, and $1500 in port work allowed them to flow just a little better than the AFR 70% CNC ported heads. I dont think $600 would be enough to get your heads to outperform the AFRs. I would buy the AFRs. I dont know about the dart numbers, but I have seen several tests done on AFR heads, and in 90% of the cases the AFR heads flowed exactly what they were advertised to.