Short answer is your CPU is better than the onboard GPU in 99% of cases.
I'd just be patient with the CPU plotting, get more ram so you can plot one file and optimize another on a different drive at the same time.
If you get over 50TB I'd consider a nice GPU for plotting / mining, but you don't need it until then. Or kick out the $150 for a 1050 and it'll be about 2x your CPU speed.