As for the casualties involved in the Arctic convoys, something from Brian Schofield's The Russian Convoys:
Allied naval casualties: 1,944 killed with 'merchant marine' casualties being 829. 811 hulls made the voyages with 58 sunk. Some 428 million pounds and 11.2 billion--yes, that's billion--dollars worth of goods (broken down by category in Schofield's volume) went to Russia by way of the northern route.
On the other hand, the Persian Gulf route through Iran (anyone still wondering about antecedents to today's conflicts in the area would be well advised to wade through this history) was able to supply as much as 3 times the monthly tonnage going by way of the Arctic.
Schofield does spend his final chapter discussing a number of the issues, including one I found interesting wrt the claim that sending fighters to Singapore in 1941, rather than to Russia, would have allowed the Allies to contain the Japanese in the Far East. I recently--and finally--got around to picking up and reading Grenfell's Main Fleet to Singapore where he levels the same argument. I find it quite unpersuasive but it's an example of how Schofield covers so many of the arguments in his final chapter.
All in all, a pretty neat topic to tear into.