Source IP rate limiting in iptables: hashlimit vs recent
Is there any difference in how these two will behave?
No, what you wrote will functionally do the same thing.
With an emphasis on performance, which one is preferable?
Arguably, recent has better performance because it maintains a table but does not use hash buckets.
Is there a significant downside to using both modules?
I'm not sure why you would use both. You would have the performance impact of using both modules when you only need one.