Thanks for coming back and providing us in-depth details of your concern, Steven_ZA.

There are no transaction limits as far as performance is concerned. The transaction complexity has more impact on performance than transaction's volume. For instance, an invoice with a single item and no sales tax is less complex than one with multiple items and with sales tax applied.

Also, QuickBooks Online (QBO) is a web-based service and it relies on your computer or device’s processing power, the amount of available memory (RAM), and the bandwidth of your Internet connection to perform. A shortfall in any area can reduce performance. To improve performance, just follow the Why is my QuickBooks Online slow? article. 

Feel free to visit our Banking page for more insights about managing your bank feeds in QBO.

I'm just one post away if you need a hand with reconciling your accounts or any QuickBooks related. I'll be here to ensure your success. You have a good one.