I tested my three full frame cameras ( Nikon D800, Leica M9 and Sony A7r) with a variety of primes.
At 24mm I tried Nikkor 24/1.4 G ED on D800 and Summilux 24/1.4 both on M9 and A7r (via adapter).
At 35mm I put Sigma 35/1.4 on Nikon, Summilux 35/1.4 on Leica and Zeiss 35/2.8 FE on Sony. I also tried Sony with the 35mm Summilux.
For "normal" focal lengths I tested Nikkor 50/1.4 G on D800 and Konica Hexanon 60/1.2 on both Leica and Sony.
All lenses were tested wide open, at f2.8 and and f8. I set up a controlled natural scene (print, details etc etc) and spent today's morning comparing the central resolution/contrast delivered by the configurations. Not scientific by any measure, but I'll be interested to compare the results later with Imatest.
All raws were developed in LR 5.3 at standard setups. Also the bodies were with standard parameters on.
The 18Mpix sensor gives Leica M9 some trouble to compete with the 36Mpix rivals . Both Summiluxes and the Hexanon gave visibly more detailed photos at all apertures on Sony A7r. On Leica they were limited by the sensor which resulted occassionally with moire--a sign that the lens "outresolved" the sensor. The same glass performed beautifully with A7r and moire was observed only once: with the 24 mm summilux at f2.8. Of course the Nikon was protected from aliasing by AA filter, had it been D800E , moire might be present there too . But the same AA/OLPF cuts the Nikon's resolution quite significantly. Leica M9 with its superb diffraction limited lenses (and no anti aliasing/optical low pass filter) performs just 15% below its Nyquist limit (maximum theoretical resolution)-see Erwin Puts site imx.nl. Losses on the Nikon and it's lenses are bigger--up to 35% (maybe 25-30% on the "E" version). In fact M9 and its glass was almost there with D800 throughout the test. And with Hexanon it managed to be better than the D800+Nikkor 50/1.4 combo.
In fact A7r tells us what Leica could achieve with a 36Mpix sensor. A7r is also devoid of the OLPF.
D800+Nikkor 24/1.4 vs A7r + Summilux 24/1.4
The summilux wins hands down at 1.4 and from 2.8 it is better than the nikkor at f8.
D800 + Sigma 35/1.4 vs A7 + Zeiss 35/2.8 FE + Summilux 35/1.4
The Sigma is currently (DxO tests) the sharpest 35mm FF lens .
Wide open at f1.4 it is behind the Zeiss at f2.8 . From f2.8 both lenses/bodies go head to head. Sharpening in Nik Output Sharpener adds to the visual impact. D800 might reach the levels of D800E with some tweaking here. In general cameras without AA/OLPF filters (A7r and M9) do not gain as much from sharpening as the ones outfitted with an OLPF.
When I put the Summilux 35/1.4 on my Sony the combo showed some advantage over both 35mm rivals . It was better at f 1.4 than the Nikon/Sigma at 1.4 and slightly behind the wide open Sony/Zeiss (2.8). From f2 it was better than the other two lenses/bodies and from f2.8 it bettered their f8 perfromance.
D800+Nikkor 50/1.4 vs A7r+Hexanon 60mm/1.2
The cheap Nikkor is not known to be the sharpest of the "normals" crowd
(I wish I could try the Otus) but at f8 it is supposed to be nothing short of very good. Or it should be.
Hexanon on the other hand is a legend. It was manufactured by Konica in a limited run of 800 pieces. At f1.2 it is a bit soft, I love it so on M8 as a portrait glass. From f1.4 it is one of the sharpest lenses I have seen.
Mounted on A7r it demolished the Nikons at all apertures. At f1.4 it is equal to Nikon/Nikkor's f8. At f2 it trashes the rival set to f8 so badly, it hurts.