Well, the point with the T version is that it's more energy efficient and in order to get that intel has reduced its clock speed from 4ghz to 2.8 ghz which is a significant difference. Also the 6700t isn't unlocked meaning that you won't be able to overclock it (not sure if you are interested in that or not). Overall the performance difference won't be huge as it's a really powerfull CPU, but it really depends on what you're using the computer for. If i where you i'd probobly wait for the i7 6700k to return in stock or you could order it online at amazon or some other place.
Hope this helps!