I would not be concerned about the length being 4 meters instead of 3 meters having any effect on performance.
Personally, I'd rather wait for the right deal to come along. 4 meters probably wouldn't sound much different than 3 meters, but why pay more for cable that you don't need. I'm sure a 3 meter run will pop up in the near future, just be ready when it does. Try placing a wanted ad. Whatever you do, don't coil the excess cable if you do buy the 4 meter run, as that will sound worse.
FWIW, I'm getting ready to list a 2.5 meter pair of Audience speaker cable.....as soon as I get my a$$ in gear and get the photos, maybe tonight. Perhaps there is someone in a similar situation with a 3 meter pair, just waiting to get motivated to sell.
Try a wanted ad, sometimes they work, I know I've bought and sold through the wanted ads.