I have discovered lately that I may need to try a larger aperature as I am having to squint too much to get the job done with the .040 I am now using.  After a few shots I can't focus on anything-too much eye strain.  For those of you who have been down this road, what size aperatures did you go to to eliminate eye strain and still maintain a decent score on the target?  I shoot a RRA DCM.  I have already ordered an .050 but haven't tried it yet.  How large is too large?  Thanks for your help.  

Over 50?  Heck, I'm 31 and have to squint too much for the .043 I have.  

I think you will be happy with the .050, it's enough of a difference to notice.  What ranges are you shooting, is this for service rifle competition?  If so, you might want to check out the "Competition/Accurate AR" forum here, there's a lot of serious competitors there that could probably give you a better answer than me.

Competition Forum

ETA:  Bob Jones makes a rear sight with interchangeable apertures you might consider as well:  Bob Jones Sights

i shoot the stock irons, and can see good enough to get by with the small hole.but if i switch to the large hole,i can't see anything of the front sight but a ghost image...and i'll shoot 16 inches left at 50 yards with the large hole...I cannot account for this, but it happens. my eyes are 52 years old,and my ability to focus is long gone.the smaller the arpeture,the more in focus the front sight is...but as you know, the less light you have ,the harder it is to even see the front sight as you go down in size.and so goes the curse of ageing...