MediaTek is steadily gaining traction over Qualcomm in the past few months with its true octa-core chipsets. We even HTC using them in their flagships, but recent rumors suggest that the MediaTek Helio X20 is plagued by heating issues similar to the Qualcomm Snapdragon 810. Sources also claimed that leading brands like HTC, Xiaomi, Lenovo along with others are moving away from the 10-core chipset for the same reason.
MediaTek took notice of the rumor and has addressed it with a response stating that the Helio-X20 has the ability to turn off 2 cores whenever temperatures exceed a predefined limit. A thermal limit has been set within the SoC which drop the 2 high profile Cortex-A72 cores during high temperatures and only the remaining 8 Cortex-A53 cores will be operational in a true octa-core fashion.
While this approach is different from throttling, which is generally followed across the industry to reduce heat, it is also a questionable method. But having 8 cores perform at high performance is much better than dropping the frequency of all the cores simultaneously, which would lead to a much-degraded performance.
This also highlights the fact that the Helio X20 could, in theory, provide great benchmark scores but perform much worse in real world scenarios during extended loads such as lengthy gaming sessions. The exact ability of the chipset can only be quantified once it is consumer ready. Until then, we will only have to reply on the synthetic benchmarks.