In 2010, Boyce was on trial at Celtic but did not receive a contract. This is unfortunate because, as I will argue in this post, Boyce might be as good a goal scorer as any striker on Celtic's current roster.
Figure 1 shows the relationship between career goals scored and minutes played for Boyce, and Celtic's current strike force (data from soccerway.com). The black line represents the expected number of goals for a given number of minutes played. Most of Boyce's seasons fall on or above the line, indicating a relatively high level of goal scoring productivity compared to Celtic's strikers, In fact, Boyce's 0.84 goals per 90 at Cliftonville FC in 2012-13 is better than any single season performance by any of Celtic's current strikers, with the exception of Leigh Griffiths this season and last season.
Figure 2, shows the individual trend lines for each player's career. As you can see, Boyce's line has the most positive slope, indicating a higher goal scoring rate at 1500+ minutes played than any of Celtic's strikers, even Leigh Griffiths.
A related question is: what did Celtic see or not see in 2010 that turned them off? This seems an especially poignant question given the parade of disappointing strikers that have been given contracts by Celtic since 2010 (Mo Bangura anyone?).