Blocking does little to nothing to reduce deflection of joists.
An oiverloaded joist will not fail straight down in deflection. It wil want to roll or twist first which then puts it in a postion where it is weaker than in perfect vertical alignment. This weaker positioning in turn lets it sag further.
The blocking does two things.
It prevents the rollover tendency, keepiung the joists in their strongest, vertical alignment.
It ties all the joist together so they act as a system/singulart unit instead of individually. I'm like a joist and you are too. You can lift more with help from your friends standing shoulder to shoulder.
But solid blocking does little or nothing to prevent deflection...or otherwise 'stiffen' floor joists.
You've admitted that blocking will " prevent joists from racking and twisting and warping..."
and since a straight and plumb joist will bear more without failing, it will provide for a stiffer floor.
The engineering agrees, too. That's why installation charts for joists specify what spans need blocking, bridging and furring. Leave it out and you don't meet the designed rating and risk failure.
But, if the question in the OP was referring to taking the "bounce" out of framed span, the answer is pretty much no. Although bridging and blocking will perform such as to make the joists under a local live load react in similar fashion, not racking or twisting, they will still deflect, although somewhat less than they would individually. They'll react a little more in concert with each other. But, if they're not designed adequately to make the span, they'll still move up & down (bounce), and blocking or bridging won't make a significant difference.
[This message has been edited by treebeard (edited February 23, 2003).]
"Will adding 2x6 blocking, perpendicular to the floor joists provide the same stiffening properties as 2x4 diagonal bracing?"
It's better to solid block.
2x4 diagonal bracing, either applied to the bottom of the joist diagonally across the joists, or as cross bracing will not have the same effects as solid bridging does.