As far as I can see, there's no point in going 3/4" unless it's all going to be 3/4" - I suppose if you could run it as a 'feeder' and some of the branches were 1/2" it might work, otherwise, I'd keep to what you have now. Remember also your choice of things like taps etc in 3/4" will probably be limited so you will end up reducing to 1/2" at the most end-use points. Also, as I understand it, your pressure will be lower if it's all 3/4" (but your flow ought to be higher)

The first response was good.
With 3/4" you will gain a number of advantages.
When someone turns on a tap, is there an annoying noise?
Is there any place where you wish you had more flow?
How many sinks, faucets, tubs, showers, washers, dishwashers etc do you have?
To know whether the advantages will be clearly visible.

Having a portion of 3/4 and a portion of 1/2 is good no matter where the respective segments are in the stream.

Reducing to 1/2 is normal and doesn't negate any of the flow advantages of 3/4" pipe.

-david

If you have 1/2 inch supplying the section you want to add 3/4 You will not be gaining anything.

it seems so in many situations, but no this is not correct. In pressurized supply lines there is a gain when you increase the pipe size. I some situations it is useful to know this, get the right pressure at the shower head after the water has traveled a long Distance. Pressure loss comes from distance and elbows.

In drain lines, it is different. Sizing is based on other factors.

This can be verified elsewhere (in other sites) easily.

Yes David the degradation of furthur pressure/volume loss can be reduced by upsizing even after a smaller size, thats not rocket science. Many homes may have a 3/4" water main feed but are (with or without PRV) and still piped in 1" to reduce additional drop.

pipe sizing in a house is determined by fixture units
there is a BIG difference between 1/2" and 3/4 piping
with out going into friction loss and lenght of runs
the general rule [and code] is that 1/2 does not serve 2
fivtures. so..a 3/4 line is run to a bathroom,a 3/4 x 1/2 tee is used for the first fixture and then a 3/4 x 1/2 x1/2 tee
is used for the next two..volume volume volume not pressure
pressure is determined at the prv..but volune, is the difference between hollering in the shower or not.
the disadvantages of using 1/2 piping instead of 3/4 is
when the toilet is flushed and you yell your head off in the shower..
I myself plumbed my 2 bath house using 1" to everything
then stubbed out the wall with 1/2..but i have a urnal with a flush valve
my wife can turn on the washer and flush the toilet. i do not holler

Got a question. My shower has 3 body sprays that never worked right because they were hooked up with the other shower heads and therefore had no pressure. I opened up a part of the wall on the outside to see what I could do. The body sprays have a 1/2" presure balance system hooked up to a regular valve coming from the shower heads. I bought a Moen 1/2" posi valve to hook up to the body sprays and separate from the shower heads. My main is 3/4" branching off to the 1/2" balance system. My question is the 1/2" posi valve has small holes inside for the water, would it benefit me to use a 3/4" posi valve to mix more water or would that just turn down the pressure. I hoped I explained this right. I cannot redo the 1/2" balancing system without taking all the tile and cement board off and really creating a mess. Thanks in advance.

its volumn that you want..what are your heads ratted at?
whats the gpm of your heads? whats the gpm of the valves?
if you want more gpm from the valve..drill the small hole out..make it bigger..BUT...BE WARNED,, if you have 4 heads spitting out 5gpm's each..it ain't gonna take long to run outta hot water..
as far as your tile..is there any way to replumb the system from the back of the tile wall..i have changed out valves before ..without tearing out tile..it is a pain.but can be done

the heads are 2.5 gpm/9.5L/min. maximum flow. The valve is a Moen Posi valve cannot find any gpm for this valve (see link)http://www.supplyhouse.com/uploads/documents/20377.pdf
The 2 water in holes are 5/16" the out hole is 3/8". I am working from the back. Both wall are tiled, the outside only half way up so I opened it up above the tile where the valve and the top of the balance system is. They don't make this tile anymore so I can't rip it out.