Hello and welcome to the forums
Well socket 775 is a dead socket now,so there is no reason to buy a new system with socket 775,if u can't afford the X58 motherboards then i think a Core i5 750 with a P55 motherboard would be good,what is your budget?
C'mon,man, are you telling me that all the quad cores are going to the bin? just because i5 & i7 are better than them? we cannot be chasing the technology it changes every second,the day after tomorrow those excellent processors are going to be in the same situation as the 775 sockets today
Apart from that,
The i5 platforms seems to be around the same price as the x48 or p45 motherboards,i dont think its a bad idea,but 1366 processors are now between 250 and 900£, which its absolutely crazy,and then we'l get i9 or something,and 1366 will be forgotten...look http://www.guru3d.com/news/intel-sixcore-core-i9-photos/
.if u know what i mean