Welcome to this user forum. @NorwichJohn
The unlimited refers to the broadband usage, not the calls. All packages come with free weekend calls only.
If you wanted free evening, or anytime calls, then that would be an extra you could add at any time.
Infinity 2 has the potential for faster download and upload speeds, provided your phone line can support it.
If you check this link it points out the differences between Infinity 1 and Infinity 2.
The packages are sold as speeds UP TO which means that your line may not be able to get anywhere near the maximum speeds of these packages so make sure it would be worth getting Infinity 2.
If you use this checker it will tell what cabinet you are on and what services it can receive and give you an estimate of the speed range that you can expect to receive.
Use your phone number. If you don't have a BT number use the address checker. It is more accurate than the post code checker which can cover more than one cabinet.
Would I be better off switching?
What package are you on at the moment?
If you are with BT, which home hub do you have?
Any increase is speed is also dependent on how your home phone wiring is connected.
You should be able to get near to the top speeds on Infinity 2 so either package would do. Only you will be able to decide if the extra cost is worth going for Infinity 2 over Infinity 1.
If there are not a lot of broadband users at your address or you don't stream multiple HD movies at the same time, download big files or play HD games, you would find that Infinity 1 will more than meet your needs.
If however you do all of the above or find in the future Infinity 1 does not suit your needs you can always upgrade to Infinity 2.