Warning: Clock uncertainty characteristics of the Stratix V device family preliminary

Stratix V support is still early, the timing models are not finalized yet and probably won't be fore another release or two

you really should upgrade to 11.1sp1 when targeting SV. the timing models will be better and support will be improved - but i expect the timing models are still considered "preliminary"

in practice Altera fmax tends to go up as the models are refined