How many is too many?

I've used the Migration Assistant to Preview my Org, but when looking at Opportunities I get a message saying: "This record could not be loaded because it includes too many formula fields with complex formulas, or too many custom fields. Ask your Salesforce administrator to remove some formula fields or simplify the formulas in use."

Yes, I do have 122 custom fields - which is just 24% of our 500 custom field limit.

Of these, 10 are formulas: 6 simple sums/IFs/CASE, 2 reference a field on another record  - and 2 which I suppose you could call complex (a date calculation to add x months to a user entered date - and another to display an image and text, based on value of another custom field)

As the error says it is either too many custom fields or too many complex formulas, can anyone clarify how many is too many?