best speaker wire for extra long runs

I have a 45 foot disctance between system and speakers. Currently I use whatever the thickest gauge Monster speaker wire is - I forget the specs. Is there an upgrade option that will not break the bank that would be a really significant upgrade from the Monster for such a long distance? The only option I have seen is from Cardas, but I do not have a sense of whether that would provide a significant step up in sound quality from the Monster. Speakers are Sonus Faber Grand Piano.
Thats a lot of speaker cable. Does your pre and amp have XLR outputs and inputs? If possible, relocating your amp closer to the speakers and running balanced between amp and pre may be a better option. Mogami XLR mic cables are quite reasonable.
For various reasons, 45 feet is about as close as I can get, but I do run balanced connections between amp and pre-amp. Now, I'm just trying to make the best out of a bad situation.
The Cardas Neutral is the best choice I know of. Occasionally a friend of mine has access to used CArdas cables and once in a while, a long set show up. Jallen
since you have balanced ic's between pre and power, as Mrderrick suggests, you would be much happier relocating your power amp and running long xlr ic's and short speaker cables. in point of fact, it is also much more cost effective. i use mogami and can highly recommend them. sorry if redundant.
With respect to Eric and Mrderrick, I think the OP made it clear he can't relocate his amp.

I'm no speaker cable expert, but I believe that over such a long run, resistance is your biggest enemy. Using the heavy gauge Monster is a good idea, but it may even be worth thinking laterally and investigating stores that sell equipment for PA and concert gear. Speaker cables at live shows often have to run over 100 feet and still maintain quality (audiophile quality I don't know); you may find they sell quality copper in heavier gauge than any hifi store might stock.

Just a thought...
I'm in the same situation as Gipp, stuck with avery long speaker run. I just started a thread in this forum asking about using NM romex cable for speaker wire. I am curious to see where this goes and will probably try it soon unless someone say's it might ruin my equipment or something.
My run was not nearly as long (19'), and it was not for my primary listening speakers; but I have had good luck with Analysis Plus Blue Oval. I'm using the cables with a Creek integrated and Audio Physic Speakers.
Cardas Neutral Reference is excellent for long runs.
I'd like to suggest Morrow SP1 speaker cable. I just changed to a 30 foot pair of these for my rear channels and they are wonderful. Huge soundstage, transparent and very dynamic.
What does a huge rear soundstage sound like?
According to this, it's all about wire gauge, distance, and speaker impedance.

If you choose to believe it, then Monoprice has some of the best prices for speaker wire. If you need 10 gauge, I recommend Blue Jeans Cable.
For my odd 25 foot situation, the Cable Co has recommended either bulk DH Labs Q10 or Vampire SPII (discontinued). They have never steered me wrong, albeit these are (or in the case of the VPI . . . were) the two larger gauge cables that they sold).

Any opinions on bulk supply alternatives? For my use, Plinius 9200 w/ Tyler Acoustics monitors/sub.