Marcel ... I'm running 4.1 and 3.4 ... there are a few of us brave souls on the rather dangerous technical frontier. Running into some aggravations but mostly this is because we are going to the 64 bit program, Windows 10 has added to some of the problems. If you are going to do any scenery design work, I'd stick with V3.4. I have to have it on my system for scenery design, but I "fly" 4.1 for my personal pleasure. When you move to 4+ things start to break for scenery design (Instant Scenery, ADE 1.75 (that only works with 4.0+), etc.
But there is some good news too. If you are just a dedicated simmer, not playing with scenery design, etc ... then I'd highly recommend 4.1. It uses all your computer's cores, it is smooth as silk, you can crank up the scenery higher than you could before. You'll see a lot of discussion about all the "problems" ... but those are not with V4.1 ... these are problems with the associated programs ... and work-arounds are being made for those.
No matter what choice you make, we are here to help you through the transition. We want you to make Misty's Place your home so you can always Return to Misty Moorings!
Doug