Hi Dzianis,
There's no convertion to or from Script view. As you started with a Graphical view better you understand the points which is "failing" with planViz and do the needful.
On rev74 a graph calculation view can be automatic/internally converted to SQL when you select the option Execute In = SQL Engine (this is SP8 naming, a.k.a enforce SQL engine on your rev).
This have potential to boost your Graphical view without any other changing.
Another thing to pay attention is that SP7 really converted internally to a SQL and then submitted the SQL through SQL Engine. This changed on SP8 as they do not create SQL but directly the access path for the SQL Engine gaining even more speed.
If I were you I should flag this and make some tests.
Regards, Fernando Da Rós