Here is light:  http://www.ebay.com/itm/Hylix-Full-Carbon-stem-31-8mm-93g-for-Road-MTB-Super-Light-with-Ti-bolts/121368763852?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D23490%26meid%3D8818142830762393295%26pid%3D100005%26prg%3D10073%26rk%3D6%26rkt%3D6%26sd%3D121399414769&rt=nc

Here is light and cheap(same brand):  http://www.ebay.com/itm/Hylix-Super-Ultra-Light-stem-Road-Mountain-bike-31-8mm-1-1-8-Ti-Bolts-99g-/121399414769?pt=US_Stems&hash=item1c43f80ff1

Depending on your riding...XC these should be fine...you might check out the offerings from iPlay

looks like only one on that page - the slx shifter and it is only 31.00
I don't see where you mention if you have 2 rings or 3
Depending on your races, maybe you could go 1 x and forget the front.

Kinda up to your riding - tight tree action and a less wide bar would be apprapo.

Found this for ya:
The reasons we have been preaching about wide bars since 1999 are that they simply give you more stability, more leverage to fight sudden jerks to the side and more leverage for cornering. A quick baseline to start from is to do a push up and experiment with hand width and find out where you feel most stable and powerful. From this starting point go out a bit wider and start working your way in. What we are looking for is for your forearms to slope outward slightly from your hands to your elbows when you have lowered your chest in a “half push-up” position (see photo below). At the widest your forearms should go straight up to your elbows when in this position.
This width will give you the optimum amount of control. From this position you can absorb shock, keep the wheels on the ground over a small drop, resist twisting/jerking forces and power you way trough a corner by getting enough counter pressure leverage to give you the right lean angle. - See more at: http://betterride.net/blog/2014/can-mountain-bike-handlebars-wide/#sthash.gaPr04By.dpuf

IP-057 is a high mount and pulls from top

I misunderstood you, I was thinking thru-axle of 12 and 15 size....you rarely hear of thru-axle for QR size.
Don't know that it will gain you anything in stiffnes.
When people talk of thru-axle's being stiffer and such, they are referring to the 12mm in the rear or 15/20 up front.
I have not heard/read any comparison's of QR to QR thru-axle.

You should go with 12mm thru-axle in the rear to get the extra stiffness.  Maybe try the crests with 32 hole if not already - give you a lower weight of 1500g...that is with the understanding of punt meaning you don't want to go with the wider ones.

So, a shimano's m988 thru-axle weighs 91g for perspective.
Looking at iPlay's thru-axle, it is an exact copy...I bet the nut would fit on there.
Looks like you could save 100g+ with extralite front and back - .24 lb

You have a race bike - why worry about weight - having a heavyish bike may benefit you for racing.
1600 to 1700 is pretty light  for good solid wheel that is wide.
Just looking around I found this about the pacenti tl28:  I was tempted by the pacenti rims but decided against them after reading threads on mtbr where people found them soft and easily damaged, also JRA list the TL28 ' for xc use only' and mentions they should be used with high tyre pressures to avoid damage.
If that is true, more reason to go with the wide carbon.
Also, with the thru-axle, you get your wheel on correctly every time.