Next spring will bring haswell and socket 1150. I would expect those motherboards to be similar in price to today's Z77 based motherboards.
Haswell will bring perhaps a 15% better price performance.
If you want your 3570K to be a 4 year chip, and I think that is reasonable, then I would return or market the B75 motherboard so you can overclock the "K".
You might as well get the benefit now.
On the used market, the Z77 motherboard prices will drop, but then so should the B75 motherboard you need to get rid of.
And... I think the sabretooth motherboards are overpriced. Most any Z77 motherboard will do the same job at half the price.