If you retune your Freeview HD setup, you'll find that channel 304 is now showing a caption indicating that it will be used to air Olympic events in HD, meaning that there will be three Olympics HD channels on Freeview (BBC One HD, BBC HD and channel 304). Of course, it doesn't match the 24 HD Olympics channels on Freesat/Sky/Virgin, but it's certainly a welcome addition for those without satellite or cable.
In my "expensive" setup, I did a recent Freeview HD test using a twin tuner PCI express card, recording 3 HD channels and 8 SD channels (more than enough to cover all of the terrestrial BBC Olympics coverage) and it didn't break a sweat using tvheadend. It ended up using 14% of one of the 4 cores of the i7 2600 CPU in the PC. In general, CPU isn't an issue when recording multiple channels - it's disk I/O. It's why the expensive setup will record to very fast SSD and then copy each completed recording to HDD serially (but with very fast hard drives).
Note that I've nearly finished getting quotes for my new 2-dish + 2-aerial setup, which is planned for installation on 11th June, at which point, major recording (mainly from Freesat) will take place and I will report back here on its progress. The aim is to record at least 30 simultaneous channels (almost all HD) and maybe more.