340 with a 3.79 stroke what you guys think?

Built well and within reason a 4" crank doesn't break blocks. If you intend on over 600-625 hp, then an aftermarket block should really be a consideration.

There are a bunch more 4" arms running around now than 3.79 arms. I'll bet there are going to be more 4.125-4.25 arms in SB than 3.79 in the not to distant future.

The 3.79 is a great build. A well thought out 4" arm is a good piece as well.