Hi there Sandy,
This is my first proper post, so here it is!
I was in the exact situation as you a few years ago, wondering about getting a double hander for salmon fishing, as i had been using my 9wt 9ft Zane on the top of the deveron, and had a lot of success with it, with all the larger trout, Grilse and salmon being picked up on size 12 stoats tails at the back end of the season.
Then one of the guys that i know let me have a play with his 13ft salmon rod and i was a convert from there. I have found that it is much easier to cover the water with a double hander, and have a guideline Le Cie 12ft 6in 8/9, this is a fantastic rod for lower water and will handle full sinking shooting heads with ease. I also got on sale a 14ft Loop opti from John Norris for half price and again this is a great rod.
I also think that after you have decided on a rod the line is very important to match to the rod, and i have given up with line ratings and just take note now of the head weight. I find that a lot of the guideline shooting heads are a great buy and work very well ( i much prefer shooting heads to a spey line ), as you can cut them to the length and wieght that you want, with shorter heavier heads for bigger tubes etc. Also they are easy to change if you don't think you are fishing the correct depth. When i got the shooting heads i would just go out try them and see if it loaded the rod correctly, if it was to heavy it would cut it back, there is a very useful powertaper calculator on the guideline site. Also Glasgow angling center are selling off the ready to go distance heads for £25 reduced from £54. The DTX shooting heads also are great, tried one of them and it left the rod like a rocket!
Also if you are looking for a good cheap rod, ebay is a great place to buy as there are 2 15ft Bruce and walker powerlites on there at the moment, looking like they will go cheap. I have also bought from the states before, and you can get some great deals from there, but need to add on the VAT also.
Also I have a guideline LPxe 11ft 8/9 that i got 2 years ago also, and i have to say that it is a very useful rod, and i just use my WF 9WT lines and it handles this with overhead and roll casts with ease, this was bought as birthday present and i was wondering how useful it would be but if you want a big single hand rod for high water, or to roll cast with they are very good. Never tried a switch line, but i think they could be a bit of a gimmick so that you spend £70 on another line.
Good luck finding a set up you like, i find it is a lot of playing around to get it right to your casting style, but that is all part of the fun!
Cheers
Mark