My new toy...some advice though please!

I finished building it a couple of weeks ago, have since changed the flats to SPDs and have a carbon riser bar....real issue is stem length. Currently at 100mm and I want to go shorter but I can't decide if 70mm will be too short. Medium frame and I'm 5'10" and like to ride a little more upright!! Advice wuld be much appreciated....
Whaddya think?
http://www.pinkbike.com/photo/1730786/
Whaddya think?
http://www.pinkbike.com/photo/1730786/
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lovely bike btw
http://www.flickr.com/photos/[email protected] ... 025278584/
Congrats!
Scott snail http://www.pinkbike.com/photo/1801990/
Klein bad attitude http://www.pinkbike.com/photo/1802002/
Thought I'd start with an existing 90mm stem (for familiarity/reference point) and then shorten to 70mm if necessary. Don't see many 80mm jobs for sale, otherwise might have just got one of them.
What's your build spec, if you don't mind me asking?
I'm currently thinking the following...
RS Pike 454 air/coil or Fox Float R 140mm forks
2008 XT brakes and chainset
SRAM X9 rear mech and shifts
XT/Hope Pro II hubs on Mavic 719 rims
Carbon bars
Carbon seatpost
Wellgo Mg1 pedals
WTB Rocket V or Pure V saddle
Spec...
Chris King headset
Mavic crossrides
Avid Juicy fives
SRAM X9 front and rear derailleurs and shifters
rockshox revelation (was a great deal on merlin)
2008 XT chainset and XT SPDs
SDG BelAir titanium saddle and a race face evolve seatopost
the stem and handlebar are Easton EA 50 but will be changed... I might give the LBS a ring and see if they have a 70mm stem I can borrow for a bit to try....
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