I have recently moved to an i7 machine with 32 GB of RAM abd the speed doubled again.
There are times when the CPU is opperating at 100% on all cores, but most of the time (as you mentioned with LDA) it is only running on a sinlgle core.
it looks like I am now getting CPU to elapsed time ratios of ~2.5:1 but the run has only just begun. I will let you know if it changes.
Another CPU upgrade dosent seem worth it considering it would only marginally increase the speed. If I went all out and got the 4000 GHz i7 it might double the speed during the single core periods, but it may also slow down the multicore parts some. I doubt it would double the overall speed...
The best solution would be for CREO to offer multicore capabilities on LDA...