Are you using RCA? That would be the easiest way to see where all your leads with opportunities are.
If you use RCA, once they become an opportunity in SFDC, you could set the stream cadence or the amount of content in the stream to a minimal amount. IE one or two emails vs. 4-5. When you send out all other emails, you can select whether or not you want it to override the nurture or not.
In your situation, I would recommend onboarding RCA so you can see where all the leads with opportunities are and how many you have. Then, I would set a much longer cadence to your stream (or add the ad hoc content to the stream) and have them receive it based on your sales cycle.
For our company, we have a very fast sales cycle. For leads in the late stage, we tend to continue to push them content through our nurtures but remove them from all the other net new outgoing emails to ensure the messages they are receiving are not going to disrupt the sales cycle. We worked with our sales team to ensure this content was approved and beneficial to closing deals.
I hope that helps!