I think the TMC435+GS7977 initial results in 4Q12 will go a long way towards determining this.
Something to consider beforehand. If GS-7977/Riba has viral relapse problems in GT1 treatment-naive patients it could be a wildly bullish event for Medivir. If the stock wasn't so illiquid, building a position might be a good hedge against downside risk in GILD. Positive data for 7977/Riba in GT1's shouldn't cause significant downside for Medivir so in this respect it would be good trade IMO.