I vote for option 2. If you are going to put an RDS on your pistol, then do it right. Having your slide milled with place the sight nice an low so that you can position your sight alignment just as if you were using open sights. The milling does not cost that much and they make cover plates for the milled section of your pistol in case you want to go back to open sights and temporarily fill in the milled section of your slide. Check out Bowie Tactical's sight or L&M Precision.
There are enough people out there with milled slides for an RDS that have no issues with them that I'd say its a pretty good bet that you will not have any reliability issues. Also, if you get the slide milled it will most likely have a better resale value if you decide you don't like it later on.
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GSSF Member, Glock Certified Armorer