Well there are lots of things you could go for. What attack chain do you want to use? Recharge and regen work great for DM/SR's. If you up recharge a lot, you need to fit in some recovery there since as your attack chain uses the higher tier powers your end consumption goes through the roof.
Regen working nicely, physical perfection is a good fit, you can use it as a mule for any healing uniques you have and slot health with heal IOs for the added regen benefit.
Firstly, Elude shouldn't be used for AV soloing ; it goes way over the softcap and the crash will leave you completely vulnerable!
The defense softcap is where you've reached 45% defense. At this point, any attack from an enemy that isn't 5 levels above you or have some form of ToHit will have their chance to hit at the minimum (which differs from the con of your enemy - minions have a 5% chance to hit you when at the softcap, for example). It's possible to reach more defense (with the Scrapper defense cap at 200.38%), but unless the two requirements mentioned above are taking effect or you're being hit by defense debuffs, Elude is practically useless.
Recharge will help you mantain an attack chain and bring Hasten up quicker to support it. With decent recharge you can use the Smite/MG/Smite/SL chain for the DM's/ best DPS. Here's the recharges required: Smite = 184% recharge, SL = 116%, MG = 234%.
Regeneration stacks extremely well with high defense! I'd recommend going for 175-350% on your regeneration rate.
HP will stack well with the scaling resistances and even provide higher regeneration! With accolades, 1700'ish HP should be enough.
Besides these aspects, though, hitting the softcap is your main goal.
Physical Perfection would assist on your regeneration slightly, but there's no need to use it for endurance as you'll have Dark Consumption, of course. I would either slot it with three Numina's (Heal, Heal/End, Heal/Rchg or +Regen/Recov), three heal mod's or simply use it as a proc mule (though, Health usually serves this purpose). Not that you shoudn't focus on your endurance, though do make sure to slot some lovely endurance reduction in the toggles. It's just that with two +Recovery procs, accolades and high recharge for Dark Consumption (and possibly PP!), your endurance shouldn't be a problem.
I hope this helps. For now, just wait for someone to post an awesome build 
Hi all,
I've got a L50 DM/SR that I'm looking to IO up for survivability.
Currently apart from the Steadfast unique Def/Res IO and a set of Gausians to softcap def he's got a mix of SO's and standard IO's.
I don't want to go for a high recharge AV killer it's for general play, what's best to go for regen?
Also is it worth speccing out of Elude and fitting in Physical Perfection?
Thanks
L50s: Tanks: Cryofission - Ice/EM - Dr Celsius - Fire/Ice - Saint George - SD/SS | Controllers: Psichosis - Ill/Kin - Major Chaos - Ill/Stm | Scrappers - Neutron Crusader - DM/SR
Currently Levelling: Angelic Blade - BS/WP Scrapper | Seeds of Destruction - Plant/Kin Controller