As mentioned in the first page by dr zeissler, the first powerpc Macs are slow. I believe that in order to play the majority of 90s games well, you need probably at least 3 computers. I have a Macintosh Performa 6116CD (aka Powermac 6100) with ppc at 60mhz. Due to 68k emulation some programs and games that are made for Motorola cpu, run very slow on ppc. Or even newer games. Some examples:
Monkey Island 1 and 2
Fate of Atlantis floppy version
Doom 2 with high quality graphics
Dark forces with full graphics and high resolution
I couldn't believe then that i cannot play well the monkey Island series. I didn't know regarding the emulation when i bought the Macintosh Performa in 2009. For me it is better to have a fast Motorola Mac than a slow PPC. My Macintosh LC475 which is not the fastest Motorola Mac runs great the above Lucasarts games. Even the Sierra online adventure games where on my PPC a system error occurs very often. So i choose the LC, it is better for me. But what saved me? The sonnet g3 accelerator. I found and installed one (500 mhz). The Performa is literally another machine. Lot faster and so responsive. It runs greatly later and more demanding games like Riven, Myst Masterpiece Edition, Doom, Dark forces and Heretic with full detailed graphics, Quake, Duke Nukem 3D and even Unreal and Carmageddon run in nice speed. It's a pizza box with no space but you may install the accelerator, more ram, bigger hard drive and fast cd rom drive (24x scsi). From a slow ppc it becomes a great fast retro Mac.
For 80s games i believe it is better to have something like a Macintosh classic or SE.
For games at the end of 90s a Power Macintosh G3 is needed especially for 3d games or an Imac G3.
Regarding the PCs i have only one Cyrix at 120mhz) which is enough for me until now. I have it next to my Macintosh Performa and i can say that on most games the Mac graphics are really better. Actually, some of them are lot better like Flashback and Civilization. The PCs have lot of games that support Roland and general midi. On the other hand Macs use music directly from cd like Colonization, The Incredible Machine 3 and Descent.
A game that disappointed me is Rex Nebular Mac version. The intro is cut, there is no speech, no spinning inventory and so less music which is great as quality where it exists. But It has smaller and prettier fonts than PC version and you may choose small or big screen. The pc version is great especially with the Roland MT32.
I think some microprose games have less features on macs. Like civilization for instance which is better on Mac but it has also less music and no animation on intro.