The temp range will apply to the Delo 10w30 no different than any other 10-30, with 145K , I would run the Delo first as some cleaning action is going to happen, moniter and see how fast it gets really dark. After 1 or 2 intervals on that , then use the GC. Intervals may not be full normal OCI. Even after that expect first use of the GC to get darl pretty quickly on intial first use. Again monitor till you feel comfortable with condition and change when you can't stand it anymore.
For your other questions hands down the GC should flow beter in extreme cold and be more shear stable. But if you use it straight off you will probably find it will solublize some deposits and get dark pretty quickly so you may not want to run it as long as a normal synthetic OCI. In other words you may find it being a short interval flush almost if the engine has not seen a synthetic before. This is all assuming that 145k engine is not the cleanest at this point.