Just my thoughts -
Having worked on both I switched from PC to Mac a few years back. Glad I did. It is purely personal preference and Im sure there are valid arguments for both.
Had a mac pro (still have mac pro) for 7 years and only thing that went wrong was I had to change a fan about a month ago, and that is 7 years of daily use. There is also the argument of Windows constant hotfixes and updates etc. Mac does have updates obviously I just found it to be a lot smoother.
There is also the issue surrounding viruses. Correct me if I am wrong but I have never had a problem with my Mac and viruses and have never had a firewall or anti virus program on my mac. PC is a different story as you know. I guess it depends if your studio machine will be connected to the internet or not.
Yes the learning curve from Sonar to Logic appeared a little daunting at first to me but in time as with everything else it comes with practice.
I would never go back to a PC and that is not because I hate PC's, I dont, I love em. built one myself. I just enjoy the solidity of a Mac system and not having to worry about upgrading every six months. I also found the Mac's to be quieter but then my PC is a monster 8 fan gaming rig lol. So will be different for you.
Its just personal preference. But I have never had any problems with the stability of the Mac - apart from that bloody 7 year old fan ofc
Whatever you choose Im sure it will be a good system. The important thing is when you have your system is not to regret not choosing the other. Each system has its merits. Guaranteed if you pick a PC you will think of something that tells you "wish I had got the Mac". Also if you get a Mac you will feel the same about a PC.
Enjoy your new system...whatever it will be. Both will have the ability to create music. The only limitations will be your imagination