In the last few days I read more than one user having issues with Crimson... I'm inclined to not upgrade yet.
In the meanwhile if someone can give a go to my miner and tell me if it still works it would be nice to know.
Did a test run today on a windows machine. Was doing 17Mhz on Quark with Catalyst 15.2(ish) drivers (290x OCed). Installed the Crimson drivers. Hashrate dropped to 13-14Mhz.
However when running Ethereum, i was running at 28-29Mhz and with the Crimson drivers i hit 30Mhz.
no clue why though..
New driver comes with a tweaked compiler which implies different instruction scheduling policies. Both differences seems to be in range for this kind of issues (Quark is a bit extreme I admit). In particular, the AMD compiler has historically been way too conservative on computation: this would often result in lower performance when latency-bound. Assuming Ethereum is this kind of problem it would benefit from a tweaked compiler. By contrast compute-bound kernels would get slower.