Apple has released iOS 6.1.3 today - with only minor changes, the modem firmware version remains the same for iPhone 5 and iPad 4 (an update here only for iPhone 4S). Essentially, iOS 6.1.3 fixes a gap that allows the phone app to be used without entering a code. Furthermore, Apple Maps for Japan has been improved - here in Germany also rather unimportant.
Whether anything else will change with iOS 6.1.3 - for example the language problems in the T-Mobile network, which some users have in the Telefon-Treff.de forum with their iPhone 5, is open. Since there was no update of the modem firmware, it can be assumed that the iPhone 5 does not behave differently in the network. I myself have no problems with my iPhone 5 and Congstar as a provider in the T-Mobile network regarding the voice quality.
iOS 6.1.3 is available as an Over-the-Air (OTA) update on supported devices - on my iPhone 5 the update was a good 18 megabytes in size and installed very quickly. How the update will affect the battery life (iOS 6.1.2 was much weaker on my device than the previous versions) will be shown. What to keep in mind: Apple closes jailbreak security holes with iOS 6.1.3 - there will be no jailbreak for devices with iOS 6.1.3 in the foreseeable future.