FWIW, I never send 8 guys. I don't even have a single play in my PB that sends 8 guys and I only have 2 or 3 that send 7. When I do blitz (which I consider sending 5 or 6 even though technically sending 4 with my 3-4 D is blitzing) it's usually a zone blitz. That's by far my favorite aspect of the 3-4. I've tried 4-3, 4-2-5, and 3-3-5, but their zone blitzes (and zone defenses in general) are extremely boring. They're almost all the same coverage, they just blitz different guys.
In the 3-4, the zones and zone blitzes have tremendous variety. IE. for a cover 2 (non-blitz) in non-3-4 they're almost always cover 2, 2 flat zones, and 3 hook zones. In the 3-4, these are just the cover 2s available:
(they all have 2 deep obviously)
2 flats, 3 hooks
2 flats, 3 hooks, 1 spy
2 flats, 4 hooks
2 flats, 2 buzzes, 2 hooks
2 flats, 2 buzzes, 1 hook
2 flats, 1 buzz, 2 hooks
5 hooks
There are 7 different coverage schemes just for a simple cover 2 zone in the 3-4. There are even more coverage schemes available for cover 2 zone blitzes and I won't even mention the different cover 3 looks (3-4 ever has a 3 deep man coverage play).
By mixing up these defenses I'm able to keep the offense off balance in both their run and pass game. The 3-4 zone blitzes (even the ones that only bring 4 guys) are very effective at stopping the read option.
EDIT:
Here's another awesome thing about the 3-4 which makes it especially nice against the option. Even though it has the same 7 guys in the box as the 4-3, it's alignment is much more like a 5-2 than a 3-4 because in most 3-4 formations the OLBs line up at the LOS. Even better, they line up outside the OTs which puts them in great position to attack the read option.