Link sticking won’t work. How I know? Because my DNS provider authenticates the sessions by IP. Every time I have to make changes to the DNS, I have to bring down 1 of the PPPOE interfaces.
ZS runs fine for me on a circa 2002 Dell desktop with 512 MB SDRAM and 2.2 GHz P4 Celeron. It never even allocates more than 200 MB RAM. The CPU load is for the most part in 10-20% range, sometimes jumping to 50-75% when there are many torrent connections.