What rocker arms should I buy?

It is not the pushrod angles. It is the angle of the rocker tip to the valve stem. The rocker tip moves in an arc, and the valve obviously does not. The arc'd motion of the rocker tip has 2 parts to its motion: 1 part is along the valve stem axis (which does what we want) and the other part is sideways to the valve stem axis (which does us no good in opening the valve). Minimizing the sideways part of the rocker tip motion means that you have minimized variations in speed of the valve motion relative to the valve speed that designed into the cam; having large variations in valve speed from that designed into the cam when you are pushing the engine to high RPM's causes valve float and other related issues.

The best GENERAL setup is where the arc of the rocker tips movement happens to be perfectly in line with the axis of the valve AT the midpoint of the valve lift. This will minimize the valve speed variations from the valve speed designed into the cam.

NOW, is it necessary? Here is when it is important IMHO:
- At high valve lifts
- At high RPM's
So if you are pushing 6-8k RPM a lot, yes. If pushing .600 lift, I would think so. If under 6k and .500" lift, I would not bother. If the scrub pattern of the rocker tip has small width, then you are fine.

Some setups work fine. I got some eBay PRW AL rockers and the geomtery was pretty darned good on Edlebrock heads (small width scrub), and this is a street engine with .500" lift and will rarely see 6k, so it was pointless to spend $$ on anything. Yellow Rose builds engines that go high RPM's and HP's and lifts all the time, so it makes sense there.