If I run 2 4s batts in series, is it easier on the esc than just 1 4s

[lutach]

What controller are you going to use? If you are going for 8S (29.6v or 33.6v fully charged), you will need a controller like the MGM 12032, 9032, 16024 or a BK 3695 (only for 2 pole motors and is limited to 42000rpm). You will also need the right Kv motor for your application. A good motor for 8S would be 1521/1Y 1577Kv (46679rpm), 1521/2D 1425Kv (42180rpm), 1515/2.5D 1650Kv (48840rpm), 1515/1.5Y 1500Kv (44400rpm) or go crazy with a 1527/1.5D 1500Kv (44400rpm). Those would be my first choices mainly because Neu are sold by rc-monster and for repair if needed, they can be sent to a US address except for the Mega. Now for the Megas (I love them) I would go with a ACn22/45/2 1380Kv (40848rpm), ACn22/35/2 1500Kv (44400rpm) or go nuts with ACn22/50/2 1200Kv (35520rpm). If you want Feigaos, they would have only the following 540 12XL 1390Kv (41144rpm) , 13XL1283Kv (37977rpm) and 14XL 1191Kv (35253rpm). If you are using mechanical brakes, you could get one of those cheap 100A 10S or 12S Asian controllers.