There's a lot more than just the packages restricting the "add on" static IP addresses.
Some FNO (Vuma) makes use of DHCP for example, or like Openserve where your ISP terminates the username within the Openserve network and traffic is routed back via IPC. (not sure if and how many ISP in SA use...
You referring to speeds or latency?
Latency to international might be poor. but you should mostly get the speeds on your link.
Depending on FNO, congestion, loss etc.
I have 500Mbps openserve on Vox and have no issues with speeds.