RE: Thundercat conversion help needed..
Perhaps if you use 2 4s packs as 8s LiPo, you could run a Neu 1521 1.5Y. It would be quite a challenge to achieve 10 minutes of run time.
Running a small prop such as a 38mm one may be your best bet to achieve your goals. Although I see it difficult to achieve 10minutes of runtime. This is FE's disadvantage.
Ryan