fly rods

[ed]

I have a question regarding a SP 9FT 5wt. I am not a very good caster so may be off base in my thinking. I used a friend's 10ft 6wt rod this summer and The 6wt seemed to turn over large dry flys  and flys with a dropper attached much better than my 5wt did or was this because the line was heavier AND the rod was a foot longer?   To save money was thinking of using the 6wt rocket taper on my 5wt 9ft SP in the future. cheaper than buying a rod - reel and line..... I could use it for large trout and small summer run steelhead???   My question is will the heaver line be bad for the rod over time or is the SP like some other fly rods that seem to work better if you go I line wt heavier?       Thank you,