Yes, I like Portra 800 and use it 'for best' in dull conditions, however, I believe it also works well in winter/spring sunshine too. The colours seem more saturated than Portra 400, which to be honest I've not been all that impressed with. Perhaps do a search on Flickr for Portra 800 and look at results from a number of different photographers and for 35mm and 120? Bearing in mind, the detail displayed will depend on what scanner they've used and the size and resolution it's been uploaded at. It should give you a feel for what to expect from the film before you press the 'buy it now' option.
Edit: Here's an example on 6x9 120 Portra 800 taken indoors hand-held on a dullish day with a 1950s Voigtlander Bessa 1 folding camera (scanned on an Epson V600 at 4800 DPI res [before I knew any better!] resized to 25cm wide and 300 DPI in Photoshop Elements to reduce the original 80mb file!). Not a wonderful photo but It should give you an idea of the grain structure and colour saturation, etc.
Edit 2: Here's a 35mm shot taken with Canon EOS-3 and 24-105 L IS on a dull, rainy October afternoon (scanned on V600 at 3200 DPI and resized to 25cm high at 300 DPI in PE again). Hope this is useful, you'll have to look on Flickr for how it works on a sunny day!