ibaxteruk,
What you are describing sounds exactly like the intended use case for Recommendations:
Recently Viewed
Customers also viewed. Popular products from favorite brand
etc...
Typically I've seen about two of these on most pages but I don't think it's a decision made due to slowness rather I think it comes from not wanting to overwhelm the customer with too many options. Recs should be able to handle this.
If this helps you don't forget to like, mark as helpful & mark as answer as that helps me Hope you have a wonderful day.
Mihnea Docea | Technical Support Consultant | Customer Experience | Adobe | (:: 1 (800) 497-0335