hi,
it sounds like you have a great test scenario that you should do with a drivetest 🙂 With qoS stats, I’m sure you could assess how badly the 3G is while it is loaded (looking at reselection %, coding scheme used, etc)
IMO if the 3G is so bad that the MS reselects the 2G, even with the most aggressive thresholds, then be it. But that has to be verified on the field.
Regards
pix