byte is definately on the mark with his post but would like to add what I have seen on my machines.
I had the same experience with v2.7 on my p2 machines. They seemed to get more and more difficult w/u's and times were running up to around eighteen hrs. I went back to v2.4 and things are back to normal @ around ten hrs with very little variation.
For the more powerful p3 machines, times are running between four and five hours fairly consistently with v2.7.
I totally agree with byte in that a 450 with completion times of between eight and nine hours would be the norm.
Remember, v2.7 is a beta that was not really supposed to be released to everyone. v3.0 should be out shortly as a final public release. Maybe it will be more consistent.
Happy crunching everbody!