...an important addition is my comp blaster is a GaP Tempest (60 degree throw) in a T4A with a remi rh safety. The 457 is VERY close to this in bolt theow and foreward safety...with a similar design nature as a T4 in the stock. The 455 sits in a Manners already, has been accurized, and comes with bells and whistles...but has the longer throw, reverse safety...tough call. What would you guys do???
I think what you really are looking at here is buying a turn key "known" rifle versus the lottery of buying a new one.
Personally, I haven't felt the slight difference in bolt throw or the reverse safety have made any significant difference for me.
My 6.5 is a Seekins Havak and my others are 700 based customs. It really depends on what the 455 shoots like...
If the 455 been ammo tested and shoots to the standard you are willing to accept that would drive the decision more for me. The early 457's I've heard about don't shoot any tighter than the 455's. I can't see there being much changing with their barrels as they are still using the same attachment system.