10FPS is fine.
40% seems high unless you aren't using substreams or it is a really bad computer for BI.
What is your "dated" system. Is it intel and if so, what i number and generation number?
I see people posting about their i7-xxxx system bogging down with less than 10 cameras so I wanted to update my setup. I have ~33 cams running on my BI system: HP Elitedesk 800 G1 tower i5-4590 @ 3.3GHz 16GB ram 12TB total purple drives for storage 30+ total cams currently - 22 cams visible in...
ipcamtalk.com
so turns out a bunch.. almost half .. didn't have direct to disc encoding on. Turning it on for all cameras dropped me back down to 25%-30% cpu usage, 8% gpu usage.
The system is a 6950x (no quicksync), 64 gigs ram, 2080ti gpu, with a fairly large storage array (6x 22tb seagate iron wolf, and a 24tb raid 0 array of 6x 4tb sd's)
I know -- it's overkill in some areas and complete underkill in others, and not ideal for BI. it's a server I built a few years ago as an experiment to virtualize a gamming system (believe it or not, actually worked), and super reliable, runs months and months on end without a hiccup. it works, and works well now that I realized the config was screwed up, though not a model of efficiency.
That said, it's on my list to build a much newer, efficient later system using a cpu with quicksync, ditch the GPU, likely reuse the mechanical discs and one of the sd's as a boot drive.