Long interconnect or short Speaker Cables

There is no right answer. In all probability, there will only be a very subtle difference in either scenarie.... most likely this difference will be inaudible. So go with whatever setup is most convenient.

You might take a look at Alpha-Core Goertz MI2 speaker cables. I have been using them for about 3 years and been extremely pleased. In your setup, the A-C Goertz speaker cable has two virtues:
1. the cable has very low impedance, so longer runs are not a problem;
2. Alpha-Core states on their web site that you can use uneven lengths of their speaker cable without causing problems.

Alpha-Core offers a 30-day money-back trial if you order from their web site, so you could try them to see if you are satisfied. Here's the link to their web page for the MI series of speaker cables:
http://www.alphacore.com/mispeaker.html

As others have said, it depends on your specific system and electronics, and differences may range from subtle to clearly audible. If the pre and amp are fully balanced, this is a no-brainer, use the long IC's and short speaker cables due to the noise rejecting benefits of balanced cables. However, 3M would be my suggestion for the practical limit of a single-ended interconnect before risking noise problems (once again - system and cable dependent). Regarding speaker cable lengths, for practical distances of about 2M to 6M, some say up to about a 50% difference in length may not be a problem. One 12-foot run and one 18-foot run should not make an audible difference, and is feasible if you are using bulk cabling. However, if buying commercial cables you may want to consider equal runs to facilitate future resale. If you have significant extra length in one cable, don't coil it.

Forgot to add, a lot of people like the Goertz cables described by Sdcampbell above. They do have low inductance, which is desirable in a speaker cable. However, they also have very high capacitance compared to many other cables, and their use at your lengths could create problems for your amps unless you use the zobel networks recommended by Alpha-Core (and available from Alpha-Core).

Thanks for the input
I will try to elaborate on my needs as I am not one for dissecting Capacitance or loads I will state what the manufacturers lists in there manuals

Cary SixPac mono-blocks
50 watts RMS. 110/Watts IHF
Input sensitivity 1.2 V for 50 watt output
Input Impedance 150,000 ohms
freq Response 15 Hz to 23 KHz @ 50 watts Output

Conrad Johnson PV 15
Gain 28.5b
Max Output 5.5 Vrms
Bandpass 2Hz to More than 100kHz
Out Impedance 200 ohms

Gallo Ref 3s
34Hz-50hz
Impedance 8Ohms
88db Sensitivity

If I could get some suggestions on what would be a good IC with a 18ft+ run
Also is it OK to use different lengths ICs?
The speaker cables will be less than 3' as the mono-blocks are now sitting next to them.

I realize that there are a multitude of choices when it comes to ether the IC or speaker cables but as I am sure we have all learned it gets rather expensive using the trial and error approch.

With the above information hopefully I can make an informed decision based on your input.
Thanks again for the help