Also did the test. Alexis kept up surprisingly.

Here's the wallet address I used with Alexis:
http://explorer.argocash.com/address/Ac6X7DPoUvt7XAMNHjwjD2Y9SPbSCwckW6

And here's for Klaust:
http://explorer.argocash.com/address/AW8QKNkyXJMRLJT81CpwBjLFHEWvDiSRTV
I have 910mh/s with Klaust and 800mh/s with Alexis

So the difference checks out. I'm switching both cards to Alexis now.

EDIT: OK I'm stupid and didn't realize I'm using a different algo (skein). I'll try with Lyra2v2 again soon and see. But at least we know that Alexis78 miner works fine with skein.