I was talking to Marty Chance over at NCRC a few years ago about a converter and we talked at length on starting line ratios. He said from his experience 7.50 was as low as he liked to see. Any lower he explained and the car becomes too aggressive and will be inconsistent and very critical of starting line conditions. I'm not saying that it can't be done, there are always exceptions to the rule but in his experience this was the practical limit he had found from god only knows how many converter sales and tech line calls. I think personally a range from 6.00 to 7.50 depending on the application is a good area to work within. Hope this helps.