First, the shaft size is different with the DB putters so the Matador Mid will become bigger. Second, you will need at least 3 inches above your hands to take advantage of the DB Attributes so you might run out of grip on the Matador Mid. and Lastly, the weight is different between the two grips so you may discover an overall heavier swing weight. Hope this helps!

So if I understand you correctly, changing the grips may add head weight, and if I want the length to be 38 "s, then in order to get the correct benefits of the putter, it would need to 42"s long? I'm 6' 4" and the standard putters are simply to short.

Changing the grip will add the "feel" of heavier head weight if you go with a lighter grip. You only need 3+ inches from whatever your desired length is, so if 38" is desired length then 41" is correct length. I am 6'5"/6'-6" tall and I have been fitted by Scotty's Gallery multiple times at 36.25" long for a standard putter...I cannot imagine going much longer than that and maintaining a proper stroke technically speaking, my Dual Balance putter is 40" long just to give me more room for experimentation, FWIW.

Good Luck!