Just trying out v5 beta, and am soon finding that a couple of aspects that are very very slow compared to v4.
Firstly, the splash screen stays up for an absolute age (2.5 minutes) before eventually getting through to the application.
Secondly, ingesting seems to take far far longer. It just took six minutes to ingest 65 D200 NEFs.
Also, though I'm not sure about this yet, it seems to take a little longer for an image to render fully (the rough preview comes up quickly, but the sharp image doesn't appear as quickly as it did in v5). Again, not sure on this yet... may not be the case.
Am happy to help with working out what is causing this.
I do store my images on a network drive, which I know will only impact response times negatively, but my experience of using PM4 with the network drive was fine... not quite as snappy when reading and rendering images as when on a local drive, but still perfectly useable (particularly since PM seems to "look ahead" and cache the next image in line).
I'm on Vista Ultimate 32 bit.