My 0.02 cents. It doesn't sound like you are going to demo these two before purchase so keep in mind my comments are based on my POV and skiing preferences.
I have much more experience with the SC9, but both are "Cross" type skis, good at speed and solid all-around. They are suitable for your level and terrain preferences. However, I don't consider them mid-to-long GS skis (although the SC9 is comfortable and capable at making GS type turns). If anything the RPM 90 and SC9 excel at feeling light underfoot and quick edge to edge. They are also very different than the skis you said you preferred. If you like a wider, Freeride ski (Legend 8000) or a heavier, "crud" ski (Speedmachine 12 or 14), then you might be disapponted in the SC9 or RPM90. Loved the Legend 8000 and the one I would buy if I lived out West (considering buying it anyway, I spend enough days out there every year). I thought the Speedmachine 14 XBS was a decent Cross/carving ski, but felt there are other, more versatile choices out there.
I am heavily biased towards the SC9. I thought it was better at speed (surprisingly good at speed, in fact) and excelled in making a variety of different turn shapes. In my opinion, the SC9 is for the slightly more advanced level skier compared to the RPM90. Since you already have the Look P10 binding (hopefully new, I don't like putting old bindings on new skis), it will match perfectly to the Dynastar (same company). You should demo to find the best length. Given your height, weight, preference for GS-type turns and no moguls, the 170 would be my best guess.
I bought the SC9 this preseason after demoing many skis the previous year. I wanted a versatile ski that was adept at making a variety of turn shapes, stable at speed, good in bumps and trees, and had precise edge grip on hardpack/ice . To me, the SC9 or SC10 fit the bill better than many other choices. I was a "Volkl snob" before I bought my SC9, so it took a lot to turn me away from buying another Volkl (5 or 6 Star).