"it'll cause a major performance hit"
Yes, it'll build far more circuits than are necesary and won't fix isolation problems.
"make my traffic more identifiable"
You'll certainly have non-standard traffic patterns.
An adversary could also try to intentionally cause denial-of-service conditions by, for example making you attempt to build a circuit to every port on a whole range of IPs, making you try to build tens of thousands of circuits and potentially causing denial of service.
An adversary could try to force you, on one circuit, to reuse another circuit. Assuming they suspect you're fetching both X and Y, at distinct IP:Port, and they have the ability to tamper with data on X or Y. They could inject an http redirect to force you to re-use the circuit used for X or Y with some tag that links the two together.
The solution isn't even a very good one, if you don't want all those feeds to be linked to a single identity, you'll need a better approach than sticking them all into a single client and trying to use some kind of contextless isolation.
Your uptime and the fetching of the set of feeds on the same schedule, you'll come back every N seconds and refetch the feed content. The size and offset of N will likely link your refetches together.
Instead you'd be better to try setting up a service that serves the news feeds locally, which you point your RSS reader at, which it itself pulls feeds in using a
Parcimonie-like system to preserve privacy, unlinkability and anonymity.