I don't think using GUESS for requeries is such a good idea. Since requeries should return only very few results, so the benefit of sending queryhits directly is very small. Besides, in total, less query messages have to be sent using dynamic searches to search the same number of ultrapeers thanks to QRP between ultrapeers. Don't forget that using GUESS, intra-ultrapeer QRP is pretty useless.

You should really test GUESS a little (you will have to disable the QueryKey for that). You will find that tcp queries come a lot closer to a global search than GUESS, because in one hour you will receive merely enough pongs to search about 1,000 ultrapeers and I found that 30-40% of them do not even answer to the query because the packet was either lost, those hosts are firewalled or not even online anymore.
The amount of Pongs that would have to be sent to allow using GUESS for global queries would be huge and there are already more pongs than many ultrapeers can handle. They have to devote 20% of their upstream for forwarding pong traffic alone.