Definitely Ikenvape for HV atties. I suggest trying his 3.5 ohm 801 Semi and 510 for 6V...
Edit: Actually, I recently got to try IKV HV306 atty, 3.5 ohm, and IMHO that is the best HV atty for 6V applications I've ever used! That would be my #1 recommendation. (David, I hope it's OK posting this on your forum, please let me know if it's not.)