i have been offered at set of edelbrock performer rpm heads, fully ported with 3 angle valve job at a reasonable price, with 1.6rr. i currently have out of the box iron gt40 heads with motorsport rr. questions: would the performance gains be that significant? i have a lunati cam 500/510. and also is there a demand for iron gt40's (i need to sell immediately after buyin new heads). thanks