Currently, I have the EZ track starter kit with 18" curves making the traditional kidney shape with a couple turnouts. I choose the Nickel Silver w/ gray road to ensure a better connectivity thru a small or larger layout.  In the near future, I will be upgrading my layout to have two main lines in some combination to run several loco's.  Although I have (1) GP-20 and (1) GP-40 locomotives, I will want to purchase and run the larger diesel and steam locomotives in conjunction with my current loco's. 

I know the minimum radius I will need to run on the inside main line will be 22" curves.  Is there a calculation I need to consider for the outer curve?  Is it as simple as going to the next size up with EZ Track?  As I understand, the sizes are as follows - 18" - 22" - 26" - 28" - 33".  I have room to go wider and longer but the outer main line will determine the overall width of the layout.   If it helps with replies, I have the NCE Power Cab system to run DCC.

Thank you in advance for your input!