I ran a Nosram equivalent 6.5 yesterday in my Durga on a 20t pinion with no worries. That gave a final ratio of 9.328 with kit 91t spur. The 501we from the chart has a 96t spur so the nearest ratio and pinion would be 9.371 on a 21 pinion.
Running a 5.5 I would start on a 20t pinion and keep an eye on the temp.
Here is a link to the chart. Hope it makes sense.
http://www.oople.com/rc/photos/cars/...-gearchart.pdf