If its just about playback, I can highly recommend Media Player Classic HC for Windows. I think I haven't seen a faster player so far. It utilizes DirectX 9 for most image rendering which results in a lot faster playback on many machines. Most players only uitilize the CPU for drawing.
Even uncompressed avi's had a lag free playback and fast seeking times from a USB 2.0 hard drive. The player is very good at caching aswell which should give you a benfit with files that have keyframes that are far apart from each other. It also has the option to always skip to the next keyframe when seeking (Options/Tweaks/Fast Seek). It also has a setting for the jump distance when seeking very long videos.
Generally for all plattforms recommendable is mplayer with a fitting GUI (there are quite a few of them out there for Windows/Mac/Linux). A little "geeky" but very powerfull.
You dont need RAID storage to seek through h.264 files fast. That only applies to really huge "raw" video files that are meant for editing. A video card that has MPEG-4 decoding supported would be good to have but normally any video card from the last 4-5 years supports that. Apart from that you dont need any special hardware, your problem is mainly a software issue.