The pre-asph has been much maligned over the years. The first version had problems with flare and performed rather poorly at f1,4. Once the second generation came out, it become an very good lens.
It has it's own signature, a bit of the "glow" shot wide open, but sharp enough. It has more filed curvature that the much larger and much more expensive 1,4 Asph. The focus plane "curves " slightly. If you aim it at something 8 feet away and focus on that object, you will find that in the edges the focus plane is closer to 6-7 feet. A curved focus plane. So, it might not be the greatest lens for architecture, shot wide open, but for "street" shooting it is perfect.
It is a vintage design, dating back to the 60's, but it survived the subsequent decades quite well.
I had the same dilemma, I had the 35f2 IV (as well as the 35/2 Asph and earlier incarnations of Summicron's) and I got the 35f1.4 Asph. Impressive lens when it came to resolution and sharpness, but way too flare sensitive. One of the few lenses that could flare badly enough to opaque out the whole negative! In the end I never trusted the lens for any critical shooting and got rid of it.
The pre-asph 35/1,4 and the 35/2 IV is a better package, in my opinion. They are smaller and both have a rather distinct signature to them.
