100 Amp Feeder SER or Romex

[jt700]

I have to feed a 100 AMP MLO panel located 140' away (In the same building) in a single family residential dwelling. I'm aware of voltage drop, and the fact that the path I need to take consist of going through thermal insulation. Plus the customer wants me to use copper. With that being said, I believe I could two ways if I was to use a cable:

If I use SER CU (I have to be aware of Article 338.10 (B)(4) for thermal insulation and the 60 degree column) it would be a #1

If I was to use romex it would be a #3, but I don't think they make it , so it would have to be a #2-3 Rx

Correct?

 

[infinity]

Copper NM or copper SE cable would both be sized at 60° C in this installation so the size should be the same.