I was a gearhead back in the late-60's and early 70's, when Hemi's were something really, really special...and quite rare. While there's many more on the road today, they're still something "special" in my old mind, and if I had one I know I'd fuss over it like a mother hen. Rational? Probably not, but I know I would. Also, I've read that the Hemi must use 5-20 oil; otherwise, the MDS won't work correctly. Now if the MDS is that finicky about oil, I don't think I'd be comfortable going 8K between changes...even with synthetic. Based on what I've read, I don't think many Hemi guys are going more than 5K.
I see. I also am happy my engine doesn't have MDS, but at the same time I'd much rather have a pushrod motor than a OHC motor, but really they are all things that make little to no difference. Both the 4.7L and 5.7L are great engines, one just has more displacement/power output.