NTA doesn't run into limitations based directly on the amount of bandwidth your connections have, it works based on the amount of individual conversations that are going across the monitored interfaces, which is measured in flows per second. There are a handful of flow calculators you can try out online but it is really hard to predict how many flows would be generated in any environment. If you already have netflow configured on a cisco device you could run "show ip cache flow" and it will tell you how many flows are being generated per second right now on any given router and then you can size your NTA installation to handle whatever amount it gives you. A saturated 10 gb link that directly connects just a few physical servers to a single storage array with jumbo frames would generate a lot fewer flows than a similar 10 gb link between two datacenter virtualization clusters hosting a few thousand VDI instances and servers.
The performance bottleneck is generally going to be in the disk speeds of whatever storage you have the NTA DB sitting on. I've personally seen NTA installations handling traffic from over a hundred of routers without issue so I couldn't tell you where the maximum lies but determining the total number of flows you want to be able to support is going to be the key element you need to look at.
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