I had a TK70 up until about a week ago. It was an amazing light, but with 8000mAh Tenergy Centura LSD D cells, I realized it had less watt-hours of energy on hand than a TK75 and if you put a battery extension to make it the same length as a TK70, the TK75 has almost 3 times the amount of watt-hours available. I can sacrifice 10kcd of throw for the much smaller footprint. That and the fact that I have a BTU Shocker, which has a copy of the TK70 head, but uses 3 lithium ion batteries. Tom E modified mine to XM-L2 U2 1C LED's on direct thermal Sinkpads and swapped in a direct drive IOS driver, among other upgrades. Using 3 Samsung INR18650-20R batteries, it was tested at 4760 lumens and 223kcd. It pooped all over my TK70.
TK75 - 48.96 watt hours w/ 4x Panasonic NCR18650B's
TK70 - 38.4 watt hours w/ 4x 8000mAh Tenergy Centura LSD D cells