My strongest ARM-based BOINC crunchers are two Hardkernel Odroid-N2+ boards, one running Android 9 PIE, the other Armbian. While the Rockchip RK3399 has two ARM Cortex-A72's and four ARM Cortex-A53's, the Amlogic S922X of the Odroid-N2+ has four ARM Cortex-A73's (@2.4 GHz) and two ARM Cortex-A53's (@2.0 GHz). So more, faster, and better high-performance cores and less, but faster, efficiency cores. Both N2+ boards have a 80mm fan under the big standard heatsink and this helps to maintain a CPU temperature below 40 degrees centigrade.
Without fan they run quite a bit hotter. Fan screws double as stand-offs.