Re: casting weight
Depending on the size of the split shot, I think you may just have an uncastable rig on the end of your flyline. With that kind of lead, you might be better off fishing a running line and doing the lob cast.
I think you'd be better off fishing a 150-200 grain Teeny type line (24' fast sinking line attached to a floating running line) to get your fly down. There's a bit of a learning curve on fishing those lines, but once you get it, its a much safer and more efficient way to swing for steelhead.