Maximum PC

Hey guys
I am currently in an upgrading cycle on my computer due to getting some birthday money and I have moved to a smaller flat and so needed to change my tower case from the massive xclio a380.
I was just looking for some advice on where I should go,
My pc is currently,
Asus p6t SE motherboard
Intel core i7 920
Nvidia geforce gtx560ti
6gb of ram
750 psu
700gb Hard drive
I am about to purchase either the corsair carbine 300r, or the fractal core 3000.
However I would like to upgrade the performance a little, and I was thinking of getting a SATA drive and either running it as a caching drive or transferring the whole hard drive across? And maybe buying another 560ti and running sli, however I don’t think the p6Tse can do SLI and was wondering if it would be fairly simple to get a newer MB that could and transfer my CPU and other peripherals??
Any advice on anything I have said would be great, I am abit of a newbie when it comes to modding up pc, but am loving learning my way through.