I use Orcad PCB designer - currently on version 17.4 which is a few years old.
I do find certain things about it clumsy and slow, but that's not especially important. What is important is that it has every possible feature I might ever need to get my job done and make a living, and for the most part it's very stable and reliable. This wasn't always the case with older versions, but I can't recall the last time I lost any significant amount of work to a bug.
Performance is OK even on my 6 year old, basic HP laptop. On a modern PC I expect it to absolutely fly.
For a small company you probably don't need CIS - I don't have it - but it might not be a bad idea to start with it when you first begin building your library.
Get the professional version if, but only if, you need the extra features. I did upgrade to it for one job that, ironically, never made it to production. With the upgraded licence comes upgraded maintenance cost, which is why I stopped paying and am now stuck on 17.4. With hindsight, I wish I'd stuck with the Standard version and kept it up to date.
Re: mechanical design, I export STEP files to give to mechanical engineers. They use Solidworks, which makes PCB CAD software look cheap. Personally I use FreeCAD for the little bits of mechanical design that I do, but that's hobby stuff, not for making a living.