I will be getting my new line and reel this weekend.  Salmon tapered Cortland.  Is it worth it to up 1 size to a 9 wght line on 8 wgt pole. The reel is an 8,9,10.  Also what does upping accomplish and is the line thicker, heavier??????

Clint, This is a question that has no clear cut answer.  Conditions, species of fish, fly size all factor in to what size line to use.  Heavy wind=heavier line.  Heavier (bigger, more wind resistent) fly=heavier line.  Bigger quarry=heavier line, sometimes.  Loading "up" to a 9 WT may be fine for salmon but not necessarily for steelhead.  Heavier line may result in a less delicate presentation.  Too light a line may pose problems turning over heavier flies.  This is precisely why you should carry a spare spool with lighter or heavier line to fashion your fishing to the conditions.  I never understood why the rod manufacturers would label their rods with the designated flyline weights without indicating the parameters for proper amount of grains need to load the rod.  Conversely, the line manufacturers should indicate the grains of their lines and the size flies you can properly turn over.

I have noticed when I bump up a weight they cast are a lot smoother well at least on the rods I use. All in a personal preference

Upping the weight will make the road load more quickly, so it may feel easier.  In the long run, this could wear out the rod more quickly.  When I used to work with Orvis, they basically said a 5 weight range with the designated one in the middle, was appropriate. I don't see where it would give you a lot of advantage with just a floater unless, as TB21 says, you are throwing really big flies (and I can throw a standard dress steelhead fly with a five weight), but it could make a big difference with sinktips and heads.  If they have try lines where you are going, you may want to dry cast with the heavier one before making the investment.
 
L13

the heavier line will load the rod faster for up close work, i personaly try to avoid that, and help in roll casting with heavy flies or added weight.
it will turn the casting to mush if you have more than 25 feet or so of line in an overhead cast.
its all about what you want out of it.
 

Mostly roll casting and I like fishing in faster water  and I tend to have to use more shot to get down that's why I thought heavier line.  A spare spool could be in the works, but not until later.   Worse case I use my old reel which is completely serviceable if needed for the lighter days. If I absolutely hate it  I can afford to go back down and keep the heavier line for a spare spool later.    Think I am going to up it.  

Remember heavy line because of its thickness creates more drag.  Too much drag will hinder your nymph presentation.

Gerry good point........ decisions, decisions.  I borrowed my buddies reel he has 9 wgt on it and I am going to try it tomorrow.

I don't know TB. If your not sinking the fly line and throwing line upstream its disadvantage toward hinder may be fatigue more then diameter drag. All fly lines are pretty fat at that stage so to me a one up doesnt create any more drag the one down. It does however get heavy throwing more rope and mending.

Really think its a better cast advantage to up one. IMO .
The real advantage to me comes at a price ..

Clint, as most have said, its all what and how you want to do . Ive been prone to upload my rods often... these days i often end up using my 11' 9 weight switch with a 9 weight floating line, or a 13' 7 weight...believe it or not i use the same line with the 7 weight... as gerry said, a heavier line can drag harder...but at the same time, i find i can mend more accurately with a heavier line...couple that with a longer rod and you can get some deadly presentations... i also prefer a natural line color... white is a favorite of mine

Add up everyones response to your thread and its plain to see that fly fishing is an art