Switched
Uno Mega
MISO --> TX
MOSI --> RX
Now I'm getting :
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.02s
avrdude: Device signature = 0x000000 (retrying)
I'm gonna probe the clock later today and verify that it's... clocking(?). Also if I recall correctly, there is something about ArduinoISP requiring different delay times for different chips. I'm however open to any opinions as to source of error.
5V needs to go to 5V. Vin feeds the 5V regulator, you will not get 5V out if you put 5V in.
I have a buck boost switching regulators that do just that w/ 90% efficiency. LMR16006 and LM2623, they're magic. 