Question about a lens

Any opinions as to whether or not I should get a Sigma 70-300 DG Macro for my K-5 IIs? I do need a lens in this range. Already have a Sigma 17-50.

Any thoughts are appreciated,

-Richard
Pentax K-5 IIs, Sigma 17-50 f2.8, LX3, Pentax MX w/Pentax 40-80 & Soligor 80-200 f4.5 lenses, Lightroom 4.2, CS5