In addition to the other things mentioned above, my take on the problem is:
If the catalytic converter is still there, it could be choked. A choked converter has all the symptoms you are mentioning. Poor acceleration (throttle response), unable to reach high speed and poor fuel economy. My Civic had the exact same symptoms but in my case it could not go beyond 120 km/h.
I was given the option to ether remove the converter or have it cleaned. I chose to have it cleaned and see if things improved otherwise it would have to be removed. New converter is about 90,000 nd beyond my budget. Cleaning the converter got it running just great. Cleaning involves removing the converter, scraping off the combustion by-products deposited on the leading face of the converter honey-comb matrix and blowing through with compressed air in the opposite direction of the exhaust flow. This process is repeated three or four times until the entire face is free from deposits. This not a text book approach to the problem but it will get the job done. I was told that the converter will get choked again. I decided to do two things to avoid that happening. One - Changed the pump from where I get my car filled. Two - Perform an "Italian tune up" two to three times a week.
Removing the converter should be the last resort as that will confuse the ECU and you may get the CEL and at worst, the ECU may go into the "limp home mode". There is one O2 sensor before and one after the converter. The output from these two is compared by the ECU. The difference in output tells the ECU that the converter is doing its job. Removing the converter will lead to the output of both sensors to be the same. The ECU thinks that the car needs tuning etc. and so the CEL light comes on and/or the engine may go into "limp home mode".
Here is a video of another way to get the converter cleaned: https://www.youtube.com/watch?v=ZO8yUfWAUl8. I am sure you have a way of watching youtube vids.