I gotta hand it to the Mac. I purchased a new mac mini which is basically the cheapest OS X system Apple offers, and 90% of the problems I was having with Spark are gone.
Even the knobs turn smoother and it's easier to select new kits or drums. The knob no longer slows me down changing instruments, no delay on loading the kits or samples with the knob. Runs super smooth I can't even believe it.
The mini has 2.6ghz intel core i7 quad, 16 gigs of 1600mhz ram, and a fusion drive. The processor and memory are mobile hardware not desktop hardware. My self built desktop PC which is relatively new has a intel core i5 2500k with 4.5ghz overclocked processor, water cooling (runs like 40 degrees cooler), 16 gigs of 1800mhz ram, and has a much faster ssd & 10,000 rpm hard drive (vs the mini's much slower ssd/5400 rpm fusion drive combo). So from these specs alone, the pc should smoke the mini.
I've tested Spark on a windows vista laptop, windows 7 desktop, and 2 different Windows 8 desktops and they all run it pretty comparably. Of course I guess i could just have crap luck with parts I've purchased to build those other machines. Who knows.
I've always like Apple products but used Windows for the last 10 years of my production life. Now I'll never go back for production at least.
I love Windows 8 interface though. I'll be using the Windows box now for programming, gaming, and I'm going to set it up as a web server.
Anyways the fluidity that I have now makes me love Spark so much more. It's just a fun and easy product to use!
This isn't meant to be a windows or mac bashing thread or anything, I just wanted to report my experiences. Everybody has their own preferences with operating systems.