IIRC, it was the 680x0's that so often had the crippled memory bus.
The slowness on the PowerPC probably had more to do with the CPU power. PowerMacs struggled to be competitive with Pentiums for integer computation, and often the PowerPC Macs were not clocked competitively against their PC brethren.
You referenced a 601... The PowerPC 601 based machines still had NuBus, which was slow compared to VLB & PCI.
All the early PowerPC had a variety of disadvantages slowing them down: 680x0 emulation blowing the processor cache at times (particularly the 603), built in graphics were generally pathetic (and often used RAM as VRAM, undermining the value of the fast memory bus for gaming... but if you installed your own card with dedicated memory that problem vanished), and a the graphics card market was skewed for desktop publishing making it very costly to get good gaming performance.
Of course Apple abused benchmark stats to make it all seem much faster than it was, but the memory bus was derived from the Motorola 88100 bus, and consequently was pretty decent (and if you think about it, the afore mentioned 486dx4 actually had a memory bus that was running about a third of CPU speed...).
Radius graphics cards used to have fantastic blit performance.