I have a question about the operation of my rig and one about mining on flypool if anyone can shed some light on them it would be appreciated!

I am mining with two cards a Sapphire r9 390x 8G and a Sapphire r9 Fury 4G (I like Sapphire cards), using 15.12 drivers, and the "updated" Claymore 12.2 (Thank you Mr. Claymore)!

1. What I notice is that in watching Zcash manager that the hash rate of the cards varies by 10% or so. the r9 fury from 408-449 (running at -I 7), and the r9 390x from 804-845 (running at -i8). I've played around with the intensity settings and these produce the best "average" hashrate in my rig. Is the variance due to mining difficulty? Is this normal?

2. When looking at Flypool's payout statistics, I notice that some blocks are "missed."  It will say payout "to block" 74157. the next entry will say payout "from block" 74159. There are usually 2 and sometimes three blocks missing during each payout. Anyone know why?

Any thoughts or help is appreciated!

Thanks in advance.

-Iza