I have 100 meg via virgin but downloads max out at only 6m download speed in Sabnzb. I have played around with number of connections and sweet spot appears to be 30. Using port 443.
any assistance would be great.
I'm on my way out atm, but will happily help you when I get back later if nobody else does. Briefly:
More connections isn't always better. Each connection adds overhead. Start low, ramp up and find the sweet spot. About 10 connections can and should max most gigabit connections, for perspective. VM routing is pretty awful, so you may need 10 to 15 connections to max 300Mbps plus on VM.
SAB was awesome in its day but it is written in Python, and is single threaded. Basically it's not going to scale well on fast connections, and is very resource hungry. Switch to NZBGet (looks and acts almost identically, but is written in C - typically returns twice the speed of Sab on the same connection and machine).
Make sure you have a setup (CPU, RAM and especially disks) that can keep up. Downloading to one disk and unpacking to another can help. SSD for the download drive is a must for very fast connections.
List your machine specs, Usenet provider, and setup (server address(es), ports, SSL or not, which cypher, etc).