u have also think to get custom cpu cooler..

what is ur ram spec u r using rite now?
for fast multi tasking go for higher speed than 1600MHz..
for higher programming load go for high capacity..

what processor model?
and what gpu u are using now?

the right way to check before u made decision..

yup casing does affects ur temperature, get those tower casing if space/mobilty is not an isu

get a custom cpu cooler, even those cheap CM cooler with 120mm fans will be better than intel stock cooler

there are few types of RAM cooler too u know

1600mhz 3ple chennel feel the different..

MHz is the speed of transfer in a second, since u r using 1366 processor, the ram can run in triple channel smoother than dual channel.. dual channel smoother than single channel..
1600mhz speed transfer rate 12.8 GB/s in a single way. 1333mhz will be 10.667 GB/s in a single way..
imagine 1600mhz run in triple way..
how to make it triple channel? buy 3 unit ram, same speed same spec, install it on same colour RAM slot.. your motherboard should have 6 slot with 2 different colour.

this reading while gaming or idle?
if u want to use custom air cooler maybe can fit, but liquid cooler have to verify the location, space and size..
advice u to do some cleaning on gpu heatsink, change the thermal paste and new thermal pad..

yeah consider high, upgrade your gpu to newer model..

sure can but on pm, here i cant make suggestion or go to this section https://forum.lowyat.net/HardwareQuestions&Answers
let me know how much is your budget?

upgrading with that budget should be enough.. if u want to change, u wont get better spec than u r using now..