Pre-amp cables of different length? Or not??

Looking to replace the interconnects from pre-amp to the two amplifiers (ie. 4 cables).

As one of the amps sits above the other in the cabinet (well ventillated and not a problem) it would only require a 1 meter cable run. The other amp would require 1.5 meters to reach.

Since I'm planning Valhalla, this 'extra' half-meter is expensive. Should I 'economize' or buy 2 of the 1.5 meter lengths?
I can't imagine that the ordinary person would hear a difference - however, since you seem to be willing to spend a lot of money to tune your system, you are probably not an ordinary person - are your really sure you have the ability to overcome the doubt you might have about the differences that might exist? If I were you I'd buy matching lengths, then you will never question your choice.
If it were me I would not buy cables of varying length. You strive as much as possible for synergy and balance in your system, but this would be one obvious way of throwing that balance off.

Are the amps monoblacks, are you bi-amping or are you running a multi channel system? Is they are monoblocks this would not require two pairs of cable. I'm just not sure what you are trying to accomplish.
Equal length cable is probably the best, and go for the shortest possible length.
Nrchy, I am vertically bi-amping with 2 channel amps. (MC352)

One amp for the left speaker, one amp for the right.

Then bi-wiring the speakers, so each driver has its own channel and speaker cable feeding it.

This way, however, requires me to feed each amp with two interconnects from the pre-amp so both channels of each amp are essentially dedicated to either the left side or the right side of the music. I leave it to the speaker crossovers to sort it out from there. hit it right on the head. Ever think of becoming a psychologist?
Jbatlanta- There is a much more economical soltn. Just parallel the inputs buy soldering a jumper across them. If you are not sure how to do it, first check with the manufacturer to make sure there is no unusual circuitry involved; if not and you're still not sure how to do it, have any repair shop do it for you. I had it done by SMcAudio when they moded my amps to Rev A, and I ran them vertically bi-amped, biwire, just as you describe. There, I just saved you at least a kilobuck (or maybe 2, those suckers are way out of my reach)!!! You're welcome ;~)
Jbatlanta - Buy equal length cables. Otherwise you will never be able to sell them when you get the urge to try something new.