I took the comments and advice to heart, and was on the watch for a 31. Was predisposed to wait for the rebates to get one, but saw a 2 month old one for sale at a good price and grabbed it this morning.
I'm excited to try it. Would love to see some pictures for reassurance in my decision.
What I've decided to do is as follows:
Sale my 40mm ltd.
Buy the 31mm ltd (just did that)
Use 31mm ltd and 70mm ltd until I can afford a 43mm ltd next.
Then add a 21mm ltd 4th for the final kit of
21, 31, 43 & 70
That gives me the a small travel kit still of 21, 43 & 70 when I really want to go light. But also the 31 when I want it.
We will see if the logic is sound.