G'day madsmac,
Split the difference and get a 7 wt, it will be plenty of rod up to salmon, dollies and rat kings and will be a good rod for lake and large stream trout, and will do the job on small streams.
The key thing with rods is that the design line weight is with the rod casting 30 feet of line, so by definition if you are starting to cast more than that ( and you will after a short while) that is the same as casting a heavier line over a shorter range. and vice versa that is a lighter line over a longer range.
Most modern graphite fly rods will quite happily cast a line either side of their nominated weight and will adequately cast two line wts either side.
Ive got a 9'6 7wt and it casts a five wt line well, particularly at longer ranges and casts a sinking six wt out of sight and over lining one wt helps in windy conditions or bulky flies. I also use this rule on my other flyrods, I often use a 5wt line on my 4wt rods to get a bit more carry into the wind or to turn large flies and have occasionally used 6wt when fishing very small streams where the casts rarely use more than 10 ft of flyline (doesnt sound much but 8ft rod + 10 ft of flyline + 7 to 10 odd ft of leader =25 feet, and on a lot of small streams that would put your fly onto the pool above the one your fishing)
I've always found the 7 to be a useful allrounder, later on if the bug really bites you will find yourself getting more rods and the next most useful steps are a 4wt or 5wt for trout and a 9/10 wt for heavy or tropical saltwater.
Spend the big bucks on a rod, next bucks on the line and then the reel.
Hmmmmm reading all this makes me wonder why I have so many fly rods
2x4, 2x6, 1x7, 1x9, 1x 11 and a 6/7 15 ft spey
and worse I would like more