Castrol Magnatec vs Petronas Syntium

Last 2 services, I used Petronas Syntium 800 semi synthetic oil instead of Castrol Magnatec. I noticed several things about it. I listed as below:

1. Performance wise - Acceleration is a little bit slow or quite sluggish really. With Magnatec, the response is better.
2. Temperature -  Having said that, using Syntium, the engine temperature is not as hot as using Magnatec. I don't have to fill up my water tank reservoir as often as before.
3. Price - a little bit cheaper.

So, I don't know what to choose for my next service due another 3 months time. Castrol Magnatec is quite difficult to find. My regular workshop is having slight difficulties to secure the supply. I don't quite understand about it. The demand is there but the supply is quite limited.