Go to Administration -> System -> System Behaviour and there's an option to specify the "Recent List Length"

Thanks Jack, although ours is already at the maximum of 40 and I would like to increase it so that the Company section has 6 entries instead of 4. I may try increasing it in the database to circumvent the validation error when attempting to increase the value beyond 40. Although it would be nice if you could be more specific e.g. Increase the COMPANY and PERSON sections on the recent menu to say 10.

Oh I understand what you're getting at. There must be a way because on our server (7.3 Patch 2) I've got 12 Recent companies, 8 recent people, 12 recent Oppo etc listed in my Recent List. Can't think of where this is being set - will do some digging...