One thing I'd like clarity on is if it's worth it to go over that 45% value to ward against -Def debuffs? So if my Def is, say, +60%, I know I'm still capped. But if I get a -15% Def debuff, am I still capped?
Super Reflexes already has a high amount of resistance to defense debuffs. So going over 45% isn't worth it, in my opinion, for that particular goal with SR.
If you're concerned about specific groups with LTs or Bosses with higher than average hit chances, then using inspirations covers that gap if you are opposed to certain Incarnate solutions. Also, those kinds of enemies are priority targets to die first while their friends whiff whiff whiff.
I would always try to build for slightly above 45% as a hedge against defense debuffs. SR has huge resistances to those, but it is important to realize that because SR's protection comes mainly from high defenses at or near the soft cap it is also much more vulnerable to defense debuffs.
A -7.5% defense debuff might get resisted all the way down to -0.375%, but for an SR at the soft cap this actually increases incoming damage by a relative 7.5%. A 7.5% increase in incoming damage is not unnoticeable. But an SR running around with 47% defense can ignore the first -40% in raw defense debuffing, which encompasses most of what you're ever likely to be hit by.
Where this was most noticeable was in things like the ITF where you're surrounded by defense debuffers, often right up to the aggro cap. The difference between 45% defense and 47% defense was definitely noticeable there: my MA/SR with slightly overcapped defenses would regularly outtank other SR that only built to 45%, or sometimes even slightly lower thinking there was no real difference.
In *most* normal content the difference is not very noticeable and you can often cover with inspirations. But that's less practical in content with wall to wall debuffers.
Nice to see you here Arcanaville :-)