Where was the K100 getting hot? If it was just under the atty it was probably from the hot atty. If it was anywhere else and the battery was not getting hot, you have dirty (corroded) K100 contact surfaces. Where the heat was should indicate where to look for that. The low resistance build drawing so much current will make that much worse than with a lower power build.
The ohm meter, 28g kanthal and Xtar vp1 are great!
You will not find any real VTC5's right now anywhere. It's important to buy from known good suppliers so you don't get fakes. The only VTCx batt I know of right now is an
Xtar branded VTC4 from RTD Vapor. If you will not go below 0.3 ohms, you will do well with Samsung 25R or LG HE2 20 amp batteries. Illumination Supply has the 25R's now for $8 I think.