The cat sounds like it had collapsed internally. It was clearly acting as an exhaust restriction which explains the blue colour from getting cooked (they aren't supposed to get super hot to burn polluting components in the exhaust gases as they rely on a chemical reaction - melting the converting matter will clog it up) You've probably gained torque as well which will alter how the engine loads up the auto trans (hence the shift rpm change) The exhaust pulse is now travelling the full length of the exhaust and will scavenge gases from the exhaust ports more efficiently which is why you're getting the 'popping' off hard throttle.

If you mess with ignition timing you should get improvements in vacuum and overall power - there is hidden power to be made by regapping the plugs, using premium fuel and dynamically adjusting the distributor timing (no timing light needed but you will need a dwell/tach meter to monitor engine rpm's) Remember to get the ECU into tune/diagnostic mode to adjust the timing.