For the money, your far far better off getting a nice used desktop off of eBay, and fitting it with an SSD.
Then get yourself a nice 24" monitor for $100-$150 and call it a day.
You can get a nice machine with a used intel Core i5 processor and 8GB of memory for $150.
Then spend $80-$100 and get a 240GB SSD.
Out the door for $400, and it will be light years ahead of what your using now. If you go the desktop route,
a $50 add on graphics card shores up that front as well.
If you want / need the mobility then you can't go wrong with a used thinkpad. T420 machines are easily
sourced for $150 ish on ebay. If you want the 15.6 screen the T520 is usually less than $50 more. If you
watch you can usually get the complete and in decent shape for that money... then all you need to do
is reinstall the OS and configure. If you do go that route, pay attention to the battery / charger situation.
You'll really want genuine OEM Lenovo battery / charger and with the charger make sure you get the
90W version and not the 65W. The 65W will work in most cases, but I've noticed decreased performance
when using the 65. Some i7 versions of these machines require the 90W adapter. The battery isn't such
a big deal. If you need a new one, get a quality OEM one for around $30