I would stick to OEM rotors mainly because of their two piece design - aluminum hat and steel rotor rings. But if you want drilled you have to go aftermarket.
Most aftermarket rotors are junk. They tend to use lower quality steel than OEM and have poor runout specs (slight warping of rotor during manufacture). Max runout allowable by BMW is 0.10mm (0.004"), so very tight tolerances and most aftermarket manufactures cut corners to keep prices low.
Centric (parent company of StopTech) has very high end facilities and are one of the few suppliers that can match or exceed OEM quality. Centric is probably your best bet if you want drilled. There are a bunch of German suppliers that are good too but I have not seen many of them making 6er rotors.
One of your DRT eBay links says Centric are their supplier so those will be OK. The other DRT eBay link are Zimmerman which are a German OE supplier to BMW, but from what I've seen those "silver coated" rotors are lower quality and will rust over time. No idea how good those R1 Concept rotors are, but they look like they may be re-branded Centric too.
Note that slotted rotors buzz a bit when you brake hard and they also eat pads faster than non-slotted. Drilled don't have these issues.
Straight lines are for fast cars...turns are for fast drivers
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