I'm not sure where you got your information from, but you seem to have quite a few things wrong, and some other things that simply don't make sense (perhaps you can explain better?).
Recalling that the difficulty is the expected number of hashes taken to solve a block,
It is not.
with current difficulty at 3007383866429, number of h
The current difficulty is 923,233,068,449 (932 million)
The current average hashes to solve a block is 4,790,315,043,600,000,000,000 (4.79 sextillion)
That's 7,983,858,406,000,000,000 hashes PER SECOND (7.98 quintillion)
and assuming we have normal CPUs with an average of 10Mh/s (this may be optimistic),
That depends a LOT on the CPU.
A high end Intel Core i7 can manage more than 60 Mh/s
The Core i5 will top out closer to 20 Mh/s
and assuming sending a transaction took 1 second of hashing,
I'm not sure what you mean by this. Generating a transaction to send typically requires less than a half-dozen hashes. At 10Mh/s that's fractions of a millisecond.
we'd have enough hash power in plain transaction sending to rival a 1% hash-power miner, if the network was sending 5 transactions per second*.
I'm not sure what you're trying to say here. If I can create a transaction with less than 6 hashes, then 5 transactions in one second will be approximately 30 hashes per second.
Compare this to the global mining power of 7983858406000000000 hashes per second and transaction creation is equivalent to a 0.000000000000000376% miner.
Is this significant enough to try and capture?
Capture? What do you mean by "capture"?
Is it even possible to do so?
I don't know. I can't tell what you're trying to do with the hash power.
* 3007383866429 = 3007383 mega hashes
3007383 / 10 Mh/s = 300738 seconds to solve a block in 10 minutes
300738 / 600 seconds in 10 minutes = 500 tps for 100% network hash power
I'm not sure what you are saying here, my I get the feeling that you've got a lot of things wrong.