I land 28" stripers on a 5 wt with out to long a fight, so I don't think that would be a problem...To me, rod size is dictated more by the size of the flies you thing you will be casting most of the time. Big streamers and poppers need the bigger rod, midges, not so much...I am sure other will have differing opinion.Good luck and welcome to fly fishing!
I would think about what type of fishing you might want to do in the future? If you think that all you will ever do is Salmon /trout, then go with the 5wt, if you might want to go after bass or something else bigger go with the 6wt... Most all of my fly fishing I get by just fine with 5 wts and 9 wts. I sometime think a 7wt would be nice when I am out on the Colorado River and am working with big flies, wind and long casts. But I also want a 13/14 wt for big tarpon and tuna... Never enough time or money!!!!If you grow to love fly fishing one rod will most likely not be enough anyways!
i guess my only worry about going for the 5 WT would be not being able to cast big/heavy streamers far distances, or is there that much of a difference between casting a 5 WT and a 6 WT?
A 5wt will turn streamers over, where you are going to have some issues I with weighted flies... They will lag a bit until you get used to throwing them and make an adjustment.... Honestly I'd recommend a 6wt... They have a little more back bone and since you mentioned Salmon the extra backbone will be at your liking.... With that said, I fish for Salmon ,Browns, Brookies, Bass,Crappies, Pike..... I've used a 5wt to target all.... But I bought a 7/8wt a few years ago and I use it for everything now.... I just like the distance I get out of it when I'm casting big flies which is what I cast 95% of the time.... The other downside of 5wts is if the wind is blowing steadily it can make for a long day.....5wts have their place and in my opinion its on a small stream casting small flies.... I know you can do he opposite because I have done it.... But once you have casted big flies with ease at long distances with a bigger weight rod you'll wonder why you screwed around with a smaller weight....
guess my last question would be do smaller sized (10-15") inch trout/salmon still feel pretty good (do they bend the rod?) on a 6 wt? i dont want overkill in the heavy rod dept. fishing for smaller class troutadditionally what would be the difference in a 8'6" vs 9'0" 6 wt? casting distance farther with the 9'? does 6 inches make a difference? will probably be using streamers/nypmhs most of the time (i will not be using dries very much) so guessing the 9 ft would be a better choice?