I've only been on this forum for 6 years, but I don't recall seeing any stock R-Spec's running 12.6's (possible? Perhaps. Perhaps a factory freak car, but I just haven't seen it on here). The best time I saw posted from a mag stock was 12.9, but the average about .2-3 faster than the 4.6 around 13.3, 13.4. The best time I saw for the 4.6 stock was 13.7. The mags are all over the place with times:
"the 4234-pound R-Spec carries 115 more pounds. The newer model was slightly quicker in a straight line: We squeezed a 5.1-second 0-to-60 time from the R-Spec and covered the quarter in 13.7 seconds at 103 mph. Our long-termer’s initial test numbers read 5.3 and 13.8 at 104" *(their long termer was an '09 which had 10 less hp than '10-11)
2012 Hyundai Genesis R-Spec 5.0 Sedan
Motortrend managed a 4.8 0-60 (which is great), but their 1/4 mile was still only 13.3.
I take it all with a grain of salt. I was headed toward an RSpec even though it didn't feel like I was getting much 'more' car. But I couldn't get with the transmission. BTR didn't have their tune then I don't believe. If buying new I'd consider the R-Spec much more (while keeping the 4.6 on the table as an option). The R-Spec is, without a doubt, the quicker and faster car (just wasn't enough quicker/faster for me at that point).