[Ethereum] Payouts from ethermine.org rate

Uncles occur when a valid block does not make it into the long-term consensus. These orphaned blocks can be caused by high network latency, so I would say that a dramatic increase in the uncle rate indicates that the block gas limit is too high, thus making the blocks too large to propagate efficiently. Alternatively, it could indicate some other slow down of block propagation, due to DDOS attacks or some other network interference.

That's pretty much impossible to answer. A driver is a hardware's soul, it has full control over the hardware and what it will do, and how it will do it.

A few things that could influence it:

• Different task scheduling, so maybe the GPU is doing something else with a higher priority than before, giving less resources to hashing.
• The driver might have a modified quality-of-service algorithm, maybe more aggressively taking care of overheating (e.g. lower its throughput faster as temperature increases).
• Different memory management that maybe does more copies in case of ethash, but less for some other task types.
• Last but not least, one version may contain a bug over the other that does some extra/useless operation that impacts performance.

All in all it's pretty much impossible to answer it properly without a deep understanding of both the hardware and the driver code itself too. Even if the driver works perfectly, it always comes down to balancing various things to achieve an optimal performance on some baseline benchmark, which may or may not lie close to the requirements of ethash.