locale support

Just a simple question regarding which locale setting applies to which type of sorting. I have two machines, production and development. The development machine has LC_COLLATE and LC_CTYPE set to C and the other has them both set to en_US.
We originally changed the development machine from en_US to C because we were having a problem with spaces being sorted in correctly. That has been fixed on the development box, but I now noticed it is sorting lower case letters after all capital letters. I would prefer that case is ignored when alphabetical sorts are completed. This type of sort is working correctly on the machine where both locales are set to en_US.
Does this mean that one of the above mentioned locales needs to be set back to en_US? I would like to have case ignored but I want to be careful not to mess up the sorting of spaces, which we have already fixed. I hate to have to test on my own and then have to reinitialize more than once! Please advise if you can.
Thanks
Jodi