Just going by how it "feels", I'd say my car at WOT will go into lock-up at a little under 6K rpms starting in 2nd gear staying locked until you let off the gas pedal. Under cruise and low load conditions it seems to lock up around 35+ mph. The higher the stall speed, the more pronounced the "locking" feeling will be. I'm sure the jolt of a loose converter suddenly locking at cruise instills panic to alot of people but there's really no way to tune for every condition you may put your car in, and occasionally it won't be the smothest feeling transition, but if you understand what's happening it's really no big deal. Also, going down the highway and cruising at any speed above 50 mph it will be locked 99% of the time, and you'll forget the loose converter is even in there. For that reason alone, I say get the converter that will get you the best 60' possible in a vehicle that has Lockup.