Class six has always (so far, not maxed companion affection yet) yielded an Ancient Small Credit Case. Also, the highest offered yield is abundant regrettably although it produces the same thing anyways. To give you some idea of the difference here, I just logged on and collected the rewards from the slicing I started before logging off, I'll go ahead and post them although I only sent one companion out on a class 6, and it was apparently not the abundant quest.
Plug the Leak, 2V-R8, Moderate Yield class 6, cost 1,415, reward 1477, time 31m 12s
The Fly on the wall, Mako, Rich Yield class 5, cost 1930, 6,405 reward, time 29m 28s
Pointing Fingers, Gault, Rich Yield class 4, cost 1250, 6,128 reward (and Mission Discovery: Scavenging 340), time 19m 22s
Note: I checked TORhead to confirm the yield types on these, and realized that apparently the reason I don't have access to higher yield class 6 missions is my level - I'm only 37. So later on class 6 will apparently be better.
P.S. I'll go ahead and edit in the proper time/cost for Plug The Leak in about half an hour.
Edit1: Due to forgetting to note purple mission find.
Edit2: Entered the exact values for cost/time on Plug The Leak.