I would say that if you are happy with the SP then keep it.
The portability is probably the best feature and based on what you stated, it's performance exceeded your expectations. If you value portability over game performance then stick with the SP. If you want to trade off some portability for more gaming performance, then go with the Y500.
I generally carry around 3 devices with me from time to time. A laptop, 4.3" smartphone and a 7" Android tablet. All of them serves different purposes. There are some overlap in capabilities, but each fills it own niche. For example, if I really had to I could read/study on the go with my 4.3" smartphone since I can easily pull it out and put it away on a crowded train. However, the size of the fonts in my textbooks are really small and while I can read those textbooks on my smartphone it takes a bit more effort to do so than on a 7" tablet. Plus I am probably straining my vision do so; okay for a short period of time I suppose, but definitely not a good thing to do in the long run.