Hey Hawk,
Have you tried operations with the Metal Core and regular rollers and found problems ?
As long as you can drive the wire without crushing it... You are ok with V-groove rollers :)
If you are running a robot you might also consider getting your wire in 500 lb kegs which might have a more positive effect on the cast and helix of the wire and therefore a better push through the assembly than knurled rollers and 44 lb spools.
Also
http://store.millerwelds.com/commerce/product?ProdID=079606Lincoln make them too :)