The 20c 5000's look like a great deal if they put out what they are rated at. Only concern I saw on those was the width. If your fabing your own tray, no problem(and plenty of room in the 8ight) but I don't think at 160mm they'll squeeze into most of the battery trays now available. At 15c, the 4100's are probably borderline on handling your amp draw requirements with 540c XL. Keep an eye on e-bay. HeCell and Enermax have been starting auctions at reasonable prices. I don't know any thing about HeCell but I got my 5000mah 4s Enermax pack for only $102 and it is rebadged Polyquest pack: Awesome! So far I have had excellent results with Enerland cells; Polyquest, Flight Power, Poly RC, Enermax..... I highly recommend them.