Well, these are just really lucky results. Normally you would expect 3 blocks a day. See it like pool mining, some blocks you find at 40% expected shares, and others get found at 300%. The disadvantage on a 300% block is a lot bigger when solo, but so is the advantage for the 40% block.
And if you have 1400kh/s divided over a few cards, I wouldn't do it. If you go solo mining without added software your cards would compete against eachother. I have my GTX670 setup in a pool so that they both bring income.

That would be a big no, the chances of finding a block without it being orphaned are too small even at the current difficulty of only 5-6. It's the same reason I don't have my GTX670 (250kh/s) set up for solo.