There is about a foot of level line at the end of most fly lines. You can cut some of that off but I don't recommend it. One weight up on your rod (any rod) shouldn't make that much difference in its casting performance. It just slows the rod down a bit and loads it more. Now if the line itself is too heavy for the presentations you want (or the fish want), then that is another story. I believe if you just give the 7-weight an honest try you'll find you like it, especially for shorter casts.
Most of my rods are up-lined by one unless the presentation just demands a lighter line.