Upgrading my Costco-HP ENVY 700-327c video capabilties

Hi
Recently I bought this desktop from Costco.
It's HP ENVY 700-327c, with the following relevant spec's:

• Intel® Core™ i7-4770 quad-core processor 3.4GHz
• 16GB PC3-12800 DDR3-1600 Memory
• 1TB 7200 rpm SATA hard drive
• Intel HD Graphics 4600
• Internal 300W Power Supply
• Expandability (Total Slots):1x PCIe (x16) 3x 

Now, I working with graphics (3D Modeling with Sketch-up) and thought this will be sufficient for me, since the strong processor and the 'not-so-bad' on-board graphic card (Integrated Intel HD Graphics 4600). Turn out I was wrong.

Heavy scenes in Sketch-Up just took too much time to render, and even navigating in a complex scene became laggy.

As far as I understand, my best option is to upgrade my video card.
I already checked options, and got with those so far:

• SAPPHIRE DUAL-X 100365L Radeon R9 270
• EVGA GeForce GTX 750Ti SC 2GB GDDR5

My questions are:

1. Is this is really needed? I mean - the spec's of this pc are really high, and it suppose to work fairly quickly. Maybe its a drivers issue I'm facing? Here is detailed summery of my PC (CPUZ generated)
2. Giving the low power output of my power supply - what is my best option? I simply want to upgrade my PC video capabilities, and limited by the budget (about 200$).

Thanks in advance.