Comparison Swatches: MAC Silver Dawn

I mentioned when I bought Silver Dawn (Magnetic Nudes) eyeshadow by MAC last month, that it reminded me of one I already own. I couldn't remember the name at the time, but it is 'Smoke & Diamonds' (Starflash). I wanted to compare the two and at first glance, I was thinking I was rather hasty with my latest purchase as they seemed spookily similar. They are almost identical in the pan, you'll be hard pushed to see a difference. Silver Dawn (the new one) is patterned and Smoke & Diamonds (an older limited edition) is the plain one. Above photo without flash and below with.
In the swatches though, it's a different story. Firstly on my fingertips, I found SD showed the twinkly sparkly bits in it more obviously than S&D and it also seemed to look more metallic than the other.  S&D looked more finely milled than SD.  
The big difference though is most apparent in the swatches. I've taken lots of photos with and without the flash and in and out of direct daylight/house lights, so you can definitely see it. SD has a brown or bronze base (yes, despite 'silver' in it's name), whereas S&D has a silvery, pewter, taupe base.  There is a taupe element to Silver Dawn too, but the brown base is strong enough to make it look completely different from Smoke & Diamonds.  Their finishes look quite similar and the difference I noted earlier in regards to the shimmer isn't as obvious in the main swatches.  I think though that SD does have slightly bigger pieces of glitter that seem more isolated than S&D, but it's very slight.   
I'm breathing a sigh of relief that I didn't just buy another shadow exactly the same! I haven't worn both within days of each other yet, to note how alike or different they look on the eyes, but certainly the swatches show little similarities.  It's not an exact dupe if you've run out of S&D, but I suppose there's the similar taupe, smokey element.  I really love wearing S&D, so am hoping SD will become much loved too.  Have you ever bought something without realising you have an almost-dupe already?