Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
The rule of thumb for choosing a switch line is the head should be approx. 3X the length of the rod. Example: 11' switch rod = 33' head.
The grain weight of line has nothing to do with the single hand line weights we all know:
3wt. 200 - 275 grains / Single hand (100gr)
4wt. 250 - 325 grains (120gr)
5wt. 300 - 375 grains (140gr)
6wt. 350 - 425 grains (160gr)
7wt. 400 - 500 grains (185gr)
8wt. 450 - 550 grains (210gr)
9wt. 500 - 600 grains (280gr)
Okay, thanks but are these heads you loop to loop to a thin running line or are they traditional fly lines but heavier? Also are they floaters or sinkers? Can't I use a floating line with one of those Versi leaders?
So if I expect to have any successes I need to suck it up and buy a line specifically designed for my 10' 6" #6 rod.
That short rod (relative to spey/switch rods) can work for you as a single hand, two hand or spey casting.
I suggest you get a integrated switch line for it. I have the Rio Versi-tip and it works well for me for TH salt water fishing, but an integrated line (without loop attachment) should work best for what you want to do with the rod.
Rio and SA make switch lines, but I'm most familiar with Orvis (made by SA). The Orvis Access Switch line should work for you and it's only $59. Most times I suggest anglers choose a line heavier with this switch line, but it depends on the rod. Try a 7wt Switch line (380gr) for your rod. Give it a fling...good luck.