Thought I'd chime in here, James. First, although it is usually VERY important to reasonably match lengths of speaker cables, there is almost no legitimacy to matching lengths of well-designed interconnects...especially noise-limiting balanced ones. Think about it. Balanced ICs are used for micing at very long lengths...and rarely equal lengths, given asymmetric recording geometries.
So, if you're contemplating true solid Ag XLRs, for example (disclaimer: I am ArgentPur.audio), I would COMPLETELY countenance making an asymmetrical pair for you in order to save considerable expense. Indeed, I've used a balanced 3M+6M XLR pre-to-power duo for decades...NEVER needing to rebalance gain etc. But DO keep your speaker cables equal unless you have oversized cables linking to VERY high sensitivity and high impedance speakers that can mask the imbalance sonically. But this much harder to accomplish....