Hi,
This is a very good question. RAW Power heavily uses the GPU. The app uses the GPU to decode the RAW, for all adjustments, and to export images. So, a strong, modern GPU is essential for this app. The recent integrated Intel GPUs are decent, but not as good as the newer discrete GPUs found in the 15 inch MacBook Pros and other higher-end machines. I suggest trying out a few machines at a retailer or Apple Store. To do that, take some RAW files (the largest ones you have) and open them in Photos and/or Preview to see how those apps fare (they don’t work quite the same way, but adjustments in Photos also uses the GPU).
I hope this helps.
–Nik