In some ways OS/2 Warp is superior to MoS and AOS4. And well AROS is free so you get your moneys worth lol
OS/2 is not that far off WB/KS 3.0 really. The multitasking is far superior to even Windows XP (try having 99% CPU load on your Windows machine AND actually trying to do some work as is normal for multitasking OS....haha never mind at least you tried. Have a nice cup of tea and wait for it to go down to 25% CPU load)
That's more of a process priority issue than anything else.
My Win XP x64 box runs at 100% constantly, and I haven't had any problems with the system being non-responsive, as long as the GUI/Basic system has a higher priority than boinc.