I've been using SPs on my Martins and Washburns for a couple of years now. In my experience they keep their tone longer than most other strings that I have used, but are a bit like alkaline batteries in that they go "off" very suddenly!

SP+ don't seem to have made it to the UK yet. I'll try them when they do, depending on the cost premium over the regular SPs. I usually pay GBP5 to 6 (USD8 to 10) for 6-strings and around GBP9 (USD13) for 12s.

The short life and skin squeak that Bob P mentions haven't been my experience, but your personal skin chemistry can be a factor in both these. I always wipe my strings and fingerboard with a lint-free clean cloth after playing, and find this extends string life.

"Life's too short to boil a string!" - in my impoverished youth I used to do this occasionally (with and without vinegar), but the damned things always seemed to break shortly thereafter, so I stopped bothering.

Can't remember the last time I broke a guitar string.

Alan