Thank you for your feedback!
The performance of the game is for sure something what still could be improved. Also I took a note about your other suggestions / reports and added them to my list.
The “end of month lag” is well known and affects everybody to a different degree, because it can have various reason. What I personally observed is that “encapsulating” a city with rail tracks can have a bad impact, as it will take the engine much more time trying to expand a city at the end of the month.
About the main connection: This restriction is in place to avoid cheating (denying car traffic between cities). Building an alternative route should work, the only limitation is the length of the bypass. If it is too long, it will not be considered.
Also you can get rid of the main connection restriction completely by activating the appropriate Mod.