Now you are talking my native language.
The first question is how are you going to present your fly? Will you be casting from shore, from a float tube, from a canoe or boat? If you will be in a floating device, then distance is not as important as control, so I'd suggest the regular fly line instead of the Spey. I like the Weight Forward line, and I have slow, medium, and fast sinking tips to cover most of the water you are talking about.
A forth option is a shooting head. With a little practice, and a knowledge of what the double haul cast is, you can get some awesome distance. I use a custom, hand spliced, line for deeper water, in the 20 to 40 foot depth. Back in the "day" when I could buy lead core line off the spool, I spliced a medium sinking line to a lead core tip for that extra depth. With a straight extra fast sinking line, like the lead core and the new lines that replaced them, you get so much belly in this type of fishing that you almost can't set the hook.
With the custom splice you get the bottom scraping depth but far less belly so you can detect and set on the strike. Yes, I originally did this for Walleye, just to prove to a friend that it could be done, but caught some many other fish that that line, now going on 25 years old, still maintains a spot in my weapons arsenal.
I'm sure others and especially Larry will have their take on this, but I hope the above helps some.
PS, I assume you will be tossing large flies, so use a 7+ weight fly rod, with a short heavy leader to turn over the extra heavy/wind resistant flies you may be using.