I just measured the Valve clearance on my brothers 06 GS500F and all the Valves are extremely tight. My thinnest feeler gauge(0.004 - 0.006) could not slide between any of the valve shims and cams.

Both exhaust shims are 2.78mm and very tight. Should I get 2.75mm shims or 2.70mm shims?

2.70

WAIT a minute!  Your feeler gauge:  Is that inches or MM?  If inches, you need a smaller one.  Specs are .0012-.0031"

My gauges are in MM and inches!

0.004 - 0.006 Inches

0.102 - 0.152 mm

Sorry about that mistake. Damn, thats the smallest I have. Where can I get even smaller feeler gauges?

the interweb

I got mine off Amazon, it goes down to .02mm and all the way up by 1/100mm.

FYI...from the factory, some shims are in-between sizes.  I had your issue too with 2.78 and them being tight.  I had to go down 2 sizes, but YMMV.

Make sure you have the right feeler gauges, and that will tell you what size to get.  Run exhaust with a little higher clearance (around .10) since exhaust tends to get tighter with age and use.

Any less than .03, and it's like tin foil.   Got mine from e-bay.  I think it came from Hong Kong or something like that.  Did the job though.

got mine from auto zone and it goes down to .04.