The end return on Elec attacks is negligible. Power Sink will get you through your end problems and allow you to skip Stamina, but it doesn't kick in until level 35.
Maybe take Stamina as you level and then use a respec or your second build to switch out of it when you get Power Sink
Softcap usually leads to lots of toggles and low recharge, which means power sink won't be up as often. 35 levels is also a long time to endure without stamina, and without any other form of end management, especially if you start picking up those toggles early.
You will most likely need stamina.
Your going to need it in a soft caped build, as you will need to run alot of stuff to keep it working for you, i built a nice Elec/3 softcaped to ranged dmg with end sapping for melee def its fairly hard to fail with :P in fact here is the build it might save you some time working on yours if you ahve a starting point alrdy at softcap.
Hero Plan by Mids' Hero Designer 1.703
http://www.cohplanner.com/
Cosmic Spark: Level 50 Natural Blaster
Primary Power Set: Electrical Blast
Secondary Power Set: Electricity Manipulation
Power Pool: Leadership
Power Pool: Leaping
Power Pool: Fitness
Power Pool: Concealment
Ancillary Pool: Electrical Mastery
Hero Profile:
------------
Level 1: Lightning Bolt Thundr-Acc/Dmg(A), Thundr-Dmg/EndRdx(3), Thundr-Dmg/Rchg(11), Thundr-Acc/Dmg/Rchg(21), Thundr-Acc/Dmg/EndRdx(48), Thundr-Dmg/EndRdx/Rchg(48)
Level 1: Electric Fence Acc-I(A)
Level 2: Ball Lightning EnManip-Stun%(A), Posi-Acc/Dmg(3), Posi-Dmg/EndRdx(5), Posi-Dmg/Rchg(7), Posi-Dmg/Rng(34), Posi-Acc/Dmg/EndRdx(37)
Level 4: Charged Bolts Thundr-Acc/Dmg(A), Thundr-Dmg/EndRdx(5), Thundr-Dmg/Rchg(13), Thundr-Acc/Dmg/Rchg(19), Thundr-Acc/Dmg/EndRdx(46), Thundr-Dmg/EndRdx/Rchg(48)
Level 6: Maneuvers RedFtn-Def/EndRdx(A), RedFtn-Def/Rchg(7), RedFtn-Def(23), RedFtn-EndRdx(25), RedFtn-EndRdx/Rchg(43), RedFtn-Def/EndRdx/Rchg(50)
Level 8: Short Circuit Erad-Dmg(A), Erad-Acc/Dmg/EndRdx/Rchg(9), EnManip-Stun%(9), P'Shift-EndMod(15), P'Shift-EndMod/Acc/Rchg(34), Erad-Acc/Dmg/Rchg(37)
Level 10: Charged Brawl Mako-Acc/Dmg(A), Mako-Dmg/EndRdx(11), Mako-Dmg/Rchg(17), Mako-Acc/EndRdx/Rchg(31), Mako-Dam%(33), Mako-Acc/Dmg/EndRdx/Rchg(34)
Level 12: Havoc Punch Mako-Acc/Dmg(A), Mako-Dam%(13), Mako-Acc/Dmg/EndRdx/Rchg(17), Mako-Dmg/EndRdx(31), Mako-Dmg/Rchg(33), Mako-Acc/EndRdx/Rchg(33)
Level 14: Combat Jumping Zephyr-Travel(A), Zephyr-Travel/EndRdx(15)
Level 16: Hurdle Jump-I(A)
Level 18: Health Heal-I(A), Heal-I(19)
Level 20: Stamina EndMod-I(A), EndMod-I(21)
Level 22: Build Up AdjTgt-ToHit(A), AdjTgt-ToHit/Rchg(23)
Level 24: Aim AdjTgt-ToHit(A), AdjTgt-ToHit/Rchg(25)
Level 26: Tesla Cage Lock-Acc/Hold(A), Lock-Acc/Rchg(27), Lock-Rchg/Hold(27), Lock-EndRdx/Rchg/Hold(39), Lock-Acc/EndRdx/Rchg/Hold(40), Lock-%Hold(40)
Level 28: Thunder Strike Erad-Dmg(A), Erad-Acc/Rchg(29), Erad-Acc/Dmg/EndRdx/Rchg(29), Erad-Acc/Dmg/Rchg(31), Erad-Dmg/Rchg(37), Erad-%Dam(42)
Level 30: Super Jump Zephyr-Travel(A), Zephyr-Travel/EndRdx(42)
Level 32: Lightning Field Sciroc-Acc/Dmg/EndRdx(A), Sciroc-Dmg/EndRdx(42), EnManip-Stun%(50)
Level 35: Power Sink Efficacy-EndMod(A), Efficacy-EndMod/Rchg(36), Efficacy-EndMod/Acc(36), Efficacy-EndMod/Acc/Rchg(36)
Level 38: Shocking Grasp Lock-Acc/Hold(A), Lock-Acc/Rchg(39), Lock-Rchg/Hold(39), Lock-EndRdx/Rchg/Hold(40), Lock-Acc/EndRdx/Rchg/Hold(43), Lock-%Hold(43)
Level 41: Stealth RedFtn-Def/EndRdx(A)
Level 44: Shocking Bolt Lock-Acc/Hold(A), Lock-Acc/Rchg(45), Lock-Rchg/Hold(45), Lock-EndRdx/Rchg/Hold(45), Lock-Acc/EndRdx/Rchg/Hold(46), Lock-%Hold(46)
Level 47: Charged Armor S'fstPrt-ResDam/Def+(A), S'fstPrt-ResKB(50)
Level 49: Surge of Power Aegis-ResDam/Rchg(A)
------------
Level 1: Brawl Acc-I(A)
Level 1: Sprint ULeap-Stlth(A)
Level 2: Rest RechRdx-I(A)
Level 1: Defiance
Level 0: Ninja Run
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There is but one truth. Time is limited. ndnw its over
As others have noted, the softcap wrinkle might be a key part of the question.
My E3 went all the way to L50 without stamina and without any major issues...
That said, these points probably also apply:
A> That was pre-I9 / IO's
B> It's a toon I played mostly Solo with some Duo - so pacing was more
relaxed.
C> Softcapping wasn't even a thought - effective attacks and standard
Blaster thinking (kill it before it can kill you) was the main priority.
D> I recently filled out the 2nd build for that toon, and it has IO's, and
Stamina. It's not really much more powerful per se, but it's a lot smoother
doing it's thing (fewer hiccups, fewer situations that go South on me, etc.).
I kept the original SO build, and it still plays surprisingly well, but the newer
build is better overall. 
As always, it depends on what you want, what you expect, and what
you'll need to meet those goals.
Regards,
4
I've been rich, and I've been poor. Rich is definitely better.
Light is faster than sound - that's why some people look smart until they speak.
For every seller who leaves the market dirty stinkin' rich,
there's a buyer who leaves the market dirty stinkin' IOed. - Obitus.
So how important is stamina in an IO'd Elec/elec build. I'll be pushing for softcap, but I could use some extra tools, but stamina would be standing in my way. Elec/Elec seems to have several endurance mod tools, so i just didn't know if I would be sorry not to take stamina all IO'd with those in place.