Woo Woo Woo Woo from Katyusha our Cairn Terrier!
Your best bet in the South Pacific is the PG. No doubt. We love Radisson cruises. And Radisson is doing their best with the PG. But all the evidence suggests you book as soon as you can because she will likely end service as a luxury cruise ship in the South Pacific at the end of 2006. And Radisson is struggling with the new owners of the ship to maintain quality for the next eighteen months.
I can't compare her to the Silversea ships. Our first Silversea cruise is this November on Whisper. But from what I've read about Whisper, and what I know from 23 days on Radisson's Voyager, be prepared for smaller cabins and a significant notch lower on the food quality chain.
But you will be cruising on an unusual itinerary. And it is MARVELOUS. Your PG day on Motu Mahana will be something you will remember for life.
I haven't yet cruised in Antarctica. I hope to. Because of the unusual itinerary, I expect to have to bend a little on the "luxury cruise" standards I expect on Radisson's Voyager and anticipate on the Whisper. But it's worth it! I think you will also have to bend a little on the PG with respect to your Silversea standards, but it will be worth it.
Patrick