I'm quickly coming to the realization that liquid yeast ABSOLUTELY needs a starter if you want a clean, quick beer.
I am right now sampling 2 recipes with similar base grains and IBU's (an irish red and an english brown). The brown was brewed a full week later than the red and was pitched with a healthy starter, the red did not have a starter. Both were fermented at the same temp. The brown is good, bordering on great, the red still has some time before I call it average...
EDIT:
BTW I brewed a Kolsch with the same wyeast as the OP last weekend. I made a 1.5L starter in a 1/2gal growler with 1.040 wort. I chilled and decanted the clear liquid. Pitched at 56F and within 6hours I had some nice airlock activity. By the next morning the temp from active ferm was creeping up to 60F so i put it in a cold water bath because on a 5.5Gal batch in a 6.5Gal Carboy, the krausen had risen to within 1" of the stopper.