The CRM WebUI provides a list called "Recent Items" starting with SAP CRM 7.0. Users can personalize the number of displayed via Personalize -> Personalize Navigation Bar -> Recent Items:
By default this Value is set to 5. It seems that there is no customizing possibility to change the default of this value for all users of a Business Role. With the help of Stephen Johannes sending this tweet I was able to provide a solution.
When you've applied the Note 1701936 - Enabling system wide personalization then you can use transaction SPERS_MAINT to set this parameters.