One I can change in about 30 seconds to a pool that I suppose runs in the thousands
Those thousands are all in the same range though - a competent checkuser wouldn't be fooled by that. (It might turn a "confirmed" into a "likely", but that's all.) The problem with open proxies is that there is no connection between the different addresses. When you can access lots of WLANs there are all within 100m of eachother, or whatever - a checkuser would probably be able to tell they were in the same city.