I'm not quite sure if assessing any performance impact based on region is actually technically possible without the complete analytical participation of the cellular service provider and any or all contractual third party suppliers.
Hoping that this might be at least some level of help though I have found an article detailing the chips in play which may be of interest to you and where their specifications might be food for further research; specifically: -
The chips that deliver the RF capabilities of a phone tend to be over
shadowed by more consumer-friendly specifications like the number of
GB of storage, or the clock speed of a processor. However, they are
critical to the user experience of the device. Because of the nature
of radio frequencies, they also require a complex number of different
components to work together in harmony – or more accurately, without
interfering with one another. Our friends at Barclays have done a
thorough job at identifying the RF design wins inside the iPhone 5s:
- RF Micro RF3763 Power Amplifier-Duplexer (PAD) for B5 / 8 Dual PAD
- Skyworks SKY77572 Band 18/19/20 Power Amplifier Device
- Skyworks SKY77810 2G/EDGE Power Amplifier Module
- Avago A792503 Band 25/3 Power Amplifier Device
- Skyworks SKY77496 Band 13/17 Power Amplifier Device
- TriQuint TQF6414 Band 1/4 Dual Power Amplifier Device
I actually tried to find some detailed technical specifications per component above; although not exact matches there are some interesting close fits listed here, if your interested.
Quite a good component resource by all accounts. http://www.alldatasheet.com