Bruce, stick with the 5000s. I don't think that the 4Ah packs would be able to keep up.

As for the Feigao, you can toast one of those within 10 minutes. It depends on your setup. I went to great lengths to be able to run mine for a 30 minute race, but it still temped at over 200 when I was done. The Feigaos run hot. No way around it. If you want to get away from the heat, get a better motor. Neu or Lehner.