My opinion on this is (and I'm sure I'll get some heat, but it's just my opinion)....
The 801 is better at 5V, but not by a huge amount over 6V.
The 901 is better at 6V, but not by a huge amount over 5V.
The 510 is great for very short blasts at 6V, but is slightly better at 5V, and really just...