As far as I'm aware the latest KM DSLR's are not compatible with the Wireless IR flash triggers (I believe to do with the ADI & Preflash system) I'll actually need to get out my wireless trigger and try it with my 7D and 5600 and see if the above is wholly true?
As for using the on board flash as the wireless trigger, I've found that the response of the off board flash is instantaneous (this is with the 7D and 5600 plus all my film dynax's and also 3500xi flash)
Sony Alpha 900, 24-70 /2.8 SSM CZ, 70-200 /2.8G SSM, HVL-F58AM
Minolta Dynax 7D+VC-7D, 7+VCG 7, 600Si+VCG 507/600 : 24 /2.8, 50 /1.4, 85 /1.4 GD, 135 /2.8 T4.5 STF, 300 /4 HS APO G, 17-35 /2.8-4D, 28-75 /2.8D, 24 -105D, 35-70 /4, 70-210 /4
1200AF N, 3500xi, 5600HSD, IRn1 , IR Wireless Flash, RC 1000L, Angle Finder