My shots aren't that great but may I make a point? It's a great distance from Moscow to St. Pete, so even though the boat docks frequently, you will be spending a lot of time on the boat, meandering down the river, passing lots of great scenics slow enough to get sharp photos. However you will be at a distance from the shore, so even though the M8's DNG's can take a goodly amount of cropping+enlarging, you might want to reconsider the 90mm. If it was me, I would leave the 50 home. I don't know your style, but I tend to shoot probably 80% of the time with a 35mm on film, and therefore the 28mm on my M8. On film I would not want to be without my 21mm, which on the M8 is the 15. 50mm on the M8 equates to a bit less than a 70mm, which I have found (after numerous outings with a 28-70 or 35-70 zoom) to be a little too short for portraits of strangers, and much too short for picking out details from a distance. I've even found a 90mm (on film) too short for my liking, and often travelled with a 135 instead. The 90 on the M8 is approximately a 120mm, which is for me a very useful length. Definitely I wouldn't leave home the p&S. There may be times when you'll feel more comfortable leaving the M8 outfit locked up on the boat, and also, you have to know if you go without a backup, Murphy's Law will haunt you 🙁
