it is always prudent to audition your system setup - amp to speaker at least.
My initial research prior to buying my 630 is that 400-700 series are basically the same, differing only in features. Wattage differences are just a mktg rating for you to recognize somewhere in the ladder is a more powerful amp (kinda give you feeling you have not been cheated for the same wattage)
In truth - there is nothing different in wattage really (even granting 10watt higher is there - that's not much - almost nil) !!!
The reason I bought 630 is the pre-outs (during that time). I doubt it is any different today.
Same is true with 1xxx-2xxx series. Zx is another series.
Go get what sounds best for your hearing in the same series (if there really differences you note), if none, the 4xx series sometimes exceed the higher models - simpler sometimes means better! Yamaha often proved this anomaly... or probably same speakers reacts differently with amps of different series (synergy).