Very interesting post Two thumbs up!

I used DRJ's code (with 1 million iterations) for my test. I tried Tony's and I'm not sure if Excel crashed on me or the code takes longer than 15 mins to run , but I wasn't about to try that again.

Intel Pentium 4
2.80 GHz Processor
778 MB RAM

(Avg Secs)
Double Quotes: 0.400507538
vbNullString: 0.400899497
Len: 0.404778894

1/10,000 of a difference between Double Quotes and vbNullString...hmmh

Made an interesting graph too. I thought I could make a mathematical analysis of the behavior, but I really can't. It looks very close to a Sine/Cosine wave (except Len, which pretty much stayed consistent)...I was hoping to find a logarithmic function ....this could have made a decent conclusion to what's the fastest (which would have been finding out what has the lowest limit).

Check it out: