so with a 40W Victory V40, which I usually run max at 1/2-2/3rds of its power at rehearsals (mostly even only at 7 w. setting), will I possibly blow my 20 W speakers if I run 2 of those parallel? Warehouse Vet 10‘ at 20W each amount to 40 W but I hear that spikes can occur and the Veterans have very small magnets…
You'll be okay at the 7W power setting; all speaker manufacturers are very conservative when applying power handling numbers to their speakers.
"Warehouse Vet 10 at 20W each amount to 40 W"
It's not as simple as that. When speakers are connected in parallel, the voltage is the same across each voice coil. When connected in series, the current is the same in each voice coil. The important thing is the speakers' total impedance matches what the amp needs to operate properly. If each speaker is rated at 16 Ohms and they are connected in parallel, 16 divided by 2 = 8 Ohms, so use one of the 8 Ohms output jacks on the amp.
If each speaker is 8 Ohms, connect each speaker to its own 8 Ohm jack.