I've gotten back the slides I took, but contrary to what I remembered, I shot from the same position instead of correcting for focal distance, so perspective of the 75/2.8 shot and the 105/2.4 shot is different.
Nevertheless, I got hold on a 105/2.4 myself. I expect it to arrive tomorrow. I'll do some comparisons afterwards and report the findings if there is interest in it.
@GarageBoy: The 110/2 is out of my budget, but that'll be probably a great choice. The 150 is to long in terms of focal length. If 150mm would fit, I would probably go for the Pentax FA 150/2.8 which is great from what I have seen so far.