Hi there
I tune my 6-string tenor, with the C paired with a high-Cs string and the A paired with a low-A string. So the tuning can be listed as G-cC-E-aA. I also tried G-Cc-E-Aa, but it didn't sound as "full".
It took a couple of weeks for the strings to "bed down", but once they had settled they sounded really good. It takes quite a bit longer to tune up properly, but my uke holds its tuning well as I took the controversial decision to change the friction pegs for machine heads.
I have also changed the tuning of a battered old baritone 6 string from G tuning to C tuning. This was a bit more of a challenge as I had to experiment with various guitar strings to get the right tensions on all strings. Result.... it souds great!
Hope this helps
Will