My neighbour has a formula 330SS with twin BBC that runs low-mid-60s. I have towed it several times behind my 2500HD, it's manageable. Have to be careful to get a trailer that loads it as low as possible due to the height.
There are four or more of these boats on the river, I know everyone is happy with the quality and performance even with twin small blocks. I don't know how they do in rougher water and have never driven one myself.
With the smallblocks, they can be bought around 200k new I think (old stock)