So you admit that your pool too favors faster miners when you specifically (incorrectly in every way except your one shortsighted emotions over statistics way) chided Slush's pool for doing so in your OP.
"Testing with" and "favoring" are two different things. We pay CPUs and GPUs the same amount for each share. We don't "favor" either one over the other.
Your pool asks the miners to keep a high Share/GetWork ratio. In order to accomplish this, your pool requests that miners process the entire solution space of every single GetWork before requesting another GetWork. This means that the slower a miner, the more likely that that miner's solutions will be Stale.
If it takes a slow miner 300 seconds (5 minutes) to process through an entire GetWork's solution space (say a Core2 Quad CPU Miner), and if a block was solved by anyone in the entire BitCoin network even a full minute after the miner requested the GetWork, then that miner has been sitting there processing for 4 full minutes completely wasting the miner's time and electricity.
This increase in Stale Processing can lead to a very significant amount of wasted processing power, wasted electricity, and lack of pay for miners.
Even the miner in the OP (~160MHash/Sec) is requesting a GetWork once every 26 seconds instead once every 5 seconds as is the default on many miners. That's 5 times longer during which the work can become Stale. Now imagine taking that 5 seconds and multiplying it by 60 to get 300 seconds for a fairly fast CPU Miner. That is 60x the time during which the work can become Stale.
So, yes, your pool favors faster miners over slower miners by requesting that miners process the entire GetWork solution space and thus giving slower miners a significantly higher percentage of Stales than faster miners.