Don't let the device running on 1Ghz for a long time. Use this only if you want to do intensive work / MyPaint. This lessens the risk of frying your chips :P 850Mhz is usually good for day to day use and will give you a boost at normal telephone behaviour. I'm using ULV for 850mhz and 1gig. Ideal should keep the voltages to stock values. This can make your N900 more stable while being overclocked, but also risks to break the hardware if something goes terribly wrong. So crashing with ULV / XLV is better than burning a hole in it with ideal. Also there was a discussion about OC'd kernels and that they would save power by doing their work faster and then going faster back to sleep mode, rather than hanging longer on workload and sleeping later. You will notice the speed boost with the Application Manager. It tends to be terribly slow at checking repository updates (enabling and disabling custom catalogs such as maemo-devel, maemo-extras).