To the OP, seeing as how you have a 135mm for 'stealth' (I'm not sure how standing well outside the frame is stealthy, a long lens would usually attracts attention because it clearly 'points' at your subject) I would go for a 'classic' lens like a 50 or 35, preferably a 35 such as the CV Skopar. It would get you closer to people. On the other hand the 75mm 2.5 Heliar is a very fine lens. Sean Reid's review comparing it with the modern Leica 75mm Summarit suggests that apart from the vast difference in price between the two the only consideration for a purchaser is which rendering do you like most, they are pretty much equal in sharpness and overall performance. This is one of CV's most under appreciated lenses.