As with everything - "it depends".
I initially had a 9' 6wt rod and I always felt like I was going to bust the rod. So this year, I opted for a 9' 8wt rod and that felt much better, although an extra foot on the rod would probably be ideal. I fished just a few miles upstream from the mouth on my first trip and all the fish I caught were fresh, and they fought like the ****ens. Second trip up, I fished upper Elk - fish were definitely in the stream longer, water was colder, and they simply didn't fight as hard. The 6wt probably would have done the trick. Fish that run can strip a lot of line out, so you might want a large arbor reel. I'll be testing that option the next time I get up to Erie, although that may be next season. Whatever reel you have, make sure it has a good drag.
For presentation, in high, fast flowing water, you may want a sinking line, along with some splitshot to get and keep the fly down. In normal flow, a floating line will work fine. I fish egg flies (sucker spawn, crystal meth, blood dots, and the like) and streamers. I like to fish an indicator with the egg flies and either dead drift the streamers, or strip them on a jerked retrieve. Clouser minnows should work too.