This was my first "high powered rig", circa August 2010
Where did you get the OpenCL-miner on August 2010?
I work for Apple in Cupertino and that's how I originally got involved with Bitcoin. A friend of mine, An Apple OS Engineer is one of the earlier adopters and got me involved. I used his version until the better ones came along. Contrary to what ArtForz claims he was not the first GPU miner nor did he ever control 25% of the network.
I know personally of a three 4850 rig in May 2010.
In May 2010, the hashrate of the global Bitcoin network varied from 70 to 150 Mhash/s: http://bitcoin.sipa.be/speed-ever.png
3 x HD 4850 are capable of 225 Mhash/s with the most optimized miners as of today: https://en.bitcoin.it/wiki/Mining_hardware_comparison
So, assuming that this person he knows wrote a poorly optimized miner running at only ~2/3rd this speed, and was online only half the time throughout May 2010, he was contributing ~70 Mhash/s, which could explain the jump from 70 to 150 Mhash/s. BitcoinEXpress's claims sound plausible.