Not all drives necessarily use more power at 7200 RPM. Some are lower power than other 5400 RPM drives. Short of installing a hybrid drive or an SSD, a 7200 RPM drive will improve performance with respect to disk-based operations. High capacity drives, however, are almost all 5400 RPM drives, but with newer technology they are much faster than old drives at the same speed. Hitachi has a 1.5 TB notebook drive and Toshiba now has one with a 2 TB capacity. Samsung has an excellent 1 TB model.
It helps to identify models in which you are interested, then visit the mfgr.'s website to locate spec sheets so you can compare.