Either can be used, Chip, but fwiw the 5506 was planning to be phased out.
The winged outlaw karts use the 5530 (which is a 5506 clocked a few degrees at the flange to better fit the QRC chassis.)
No. It moves the powerband up is all. If you're oval racing right against the rev limiter on a momentum oval where you scrub very few rpm, then I prefer the candy cane pipes over the ones that turn behind the seat. For any track that you need a wider power band and more power at lower rpm, the 5507 (or 5511) is a better choice in my opinion.