Originally Posted by
dsbrantjr
Since you seem to have been able to shift into big-big (test this gently, while turning the crank by hand) you should be OK, but it is better to err on the long side, as a slack chain will not break anything.
^ This.
I just added a 40t cog and tried out the old chain on the stand. It shifter into big-big, but it was close. When going to the new chain, I broke it a couple links longer. Shifted better and had more peace of mind.
When in doubt always break a chain longer first, then see how it works. It is easier to remove links than add.
For your situation, I would have gone a couple links longer.
John