I was running ZS on P4 Celeron 2.2 GHz for almost 10 years, and just migrated to Atom 1.6 GHz and with 25 MBit connection my CPU utilization is hovering around 5-7% on a LAN with 11 machines permanently and a couple of visiting laptops. Our d/l volume is anywhere between 300 MB and 1 TB depending on a month.
If you were pinning Athlon 64 at 100% CPU, something was very wrong in the hardware setup. I would suspect a Realtek NIC first, this is probably the most likely culprit as their chips are horrible for sustained network traffic applications.
I always use Intel based NICs and now with Atom I installed a PCIe 1x card for LAN and this setup runs very cool, uses little CPU and only 90 MB of RAM.
I am always (with any software) trying to stay at least 1 major version behind to have something which is patched and bug-free. The migration to Atom also installed 3.5 where previously I was on 1.0, then 2.0 then 3.0. Cannot recall any show-stopper bugs, these run fine and create no issues except a minor one with VOIP which I eventually figured out
It is true that Fulvio is not frequenting this forum and seldom responds to the posts, but this is his project and he made no commitments to provide any sort of support, so we should be grateful to him for putting together an excellent router package that allowed so many of us to stay online for free for so many years and advance our own goals. Kudos to Fulvio for all the effort he spent and hopefully we are going to see more user-requested features implemented in the future!