Creating large webgraphs on the command line

Question

Am I going about this this right way?

I have a file called input.txt that has data like this:

digraph G {
rankdir=LR
node [shape=box style=filled]
A->B
A->C
A->D
B->D
C->E
E->F
}

I then input that into dot.exe which creates the data.dot file:

C:\Graphviz\bin\dot.exe < input.txt > data.dot

Then I input the dot file back to create my svg file:

C:\Graphviz\bin\dot.exe -Tsvg data.dot > data.svg

It seems to work for a small amount of data in the input.txt file, but it seems to fail with larger data sets.

I replaced dot.exe with sfdp.exe but it creates nodes that overlap each other.