Look at photo #5.
That's what I've been using for 90 deg. Lowes and Home Depot sell them.
For orginal poster, I'm working on a house right now that someone tryed using all 1/2, at the end of the line the water just barly comes out of the tap, there's so little water coming out of the shower head it's hard to rince off.
There's very little differance in cost between 1/2 and 3/4 but well worth the extra money.
When I redo the plumbing I'm going one step further and using 1" as my main and step down to 1/2 for my supplys.
It's volume you need not pressure really. If there is no volume the pressure will drop as soon as a tap is opened.