Hi!
How much is 30 degree Farenheit in Celsius??? I have run Italian Super Tigre engines at -10-15 degrees Celsius without doing anything besides setting the needles.
Most likely your Super Tigre running needs a low speed adjustment.
There is nothing wrong with a Super Tigre carb or with any other carb on the market and using 5% nitro fuel is perfect for it.

But...To have it run good you follow some simple rules, besides setting the low speed needle correctly.
1. Follow the tank position rule.
2. Use a 300cc tank
3. Use a OS 8 or Enya 3 glowplug.
4. Use a 11x6-13x4 prop. RAM or APC, and balance the prop.
5. Use a Uni-flow tank set-up.
6. Place the tank as close as possible to the firewall.
7. Use an aluminum spinner nut instead of cheap plastic spinner.