I just did a few timing tests on my computer and both V4 and V5 seemed to take around 2-3 seconds to open. I tried it about 5 times with each one but the time didn't change much.
Just to check, is it possible that there is more data loaded in the V5 versions? For example, having many more models or profiles loaded could certainly cause it to open slightly slower.
One good test could be to try going to Help > Reset All Settings (after you backed up and profiles or settings you need) and seeing if that suddenly makes the software open faster.
Can you also include your full computer specs? I'm sure that can also make a difference in the open time.