An SSD and 8GB RAM will surely help the performance. But I have doubts on the Intel Core M Chips. Sure they're designed for portability and longer battery life, but at the price of performance.
I think the benchmarking results on these chips will be in the range between an Intel Atom Chip and that of a Core i3. I doubt that it will yield results close to that of an i5.
Also could this Macbook encounter overheating problems because of the lack of fans? Especially since screen's resolution is Retina, the integrated GPU will have some work to do, especially when watching Full HD Videos, so they will be needing to limit the CPUs full potential processing power.