Had to reread to catch the "not exceptionally fast" ... is s/he fast enough that the work gets done predictably? I find that from a business perspective predictable, and generally accurate time tables are more important than absolute throughput. Now if this person is putting less than half the work than his nearest peer is, then I might have issue.

All said though, if the work is getting done and in a timely manner, then it shouldn't matter. In reading through this thread, I've been thinking, if I could get two mid-level dev positions, I could pretty easily do both at a mid-level quality/pay which combined would be more than my very senior level is currently.