Re: 10 and 12 wt
I've got a 9' 10wt Sage Flight which is a great caster. Just built a 9' 10wt MHX Kit.
I'm 57 in good physical condition but either will cause me some real fatigue after hours of blind casting. The line and rod simply weigh morethan a 8 or 9wt. The Flight would be my choice of these two. I think the BVK in this application would be a great choice too.
We used 8wts for sight casting for reds this spring break but the wind and size of the fly made would have made a 10wt more practical.
I am planning on building a 12wt as we will be chasing Ling (cobia), Jack Crevalle with slim chance of good sized tarpons this summer. Here you could easily be "under-gunned" with a 10wt if a brusier shows up. For me rod strength is an issue ever distance casting is less the concern, 40-60ft is aok. I like the comment above about a rod with backbone and bit softer tip here for mid short to mid range accuracy.
However every 12wt I've cast are the next magnitude up in casting effort over a 10wt. IMHO it's more like stepping from 5wt to 9wt in change in effort.
The 12wt is a much much less used rod (my sons think of the 10 & 12's like elephant guns) so possibly go with a guide and try his tackle out first.