SP or RP for last pitcher spot

[Dans]

I'm in a 12 yeam 5x5 roto league. We start 9 pitchers each week and they can be any combo of SP/RP. My 6 SPs are Schilling, Beckett, Harden, J. Thompson, Millwood, and N. Robertson. My RPs are Dotel, Kolb, Guardado, and M. Gonzalez. Should I start Robertson or Gonzalez as my last pitcher? I'm afraid that if I only start 5 SPs I will have trouble competing in Wins and K's, but Gonzalez has far superior ratios than Robertson. Any thoughts? I'm thinking most of the teams in my league will start 6-7 SPs. Oh, and we change our lineups weekly.