That would depend on how much ram you have as well.I would think OS 8.6 would be your best choice for speed. It will run OS 9 but very slow.If I remember right you can swap the motherboard in the 5300 for a 5400 motherboard(which vfxweb.com for sale has complete with ram and modem for $12).Check out Low End Mac: How Much Mac Do You Need? for a lot more info on these older machines.