If your weight is ample then the 456 is stronger but it depends if you ride heavily and jump etc.
The slot dropout lets you go singlespeed. You need to try it once… But the slots have the minor disadvantage of being slots rather than vertical dropouts. I don't think many have found a problem with this but you may need to run chain tugs to keep the wheel in place and it is slightly harder to get the wheel out.
I ran my 456 with 100mm forks for years and it was great. I know run it with 140mm forks and it's great. Think you can run the slotdrop at 130mm
My 456 comes in at about 30lbs the 19" is something like 5 and a bit pounds not sure abot slotdropout.
If I had to buy one now, personally I'd be going slotdropout because of the weight benefits, singlespeed options and colour.