As has been said, the area around the M42, M6 and A45 can get very busy during morning and evening rush hour, particularly if an event is on at the NEC.
If I was doing this trip I would come off the M42 slighlty earlier (say junction 8 near Water Orten) then head in south westerly direction through Castle Bromwich, Shard End, Stechford and approach Yardley from the North.
If you look at this map here, and zoom out a little, you can see what I mean.
http://maps.google.co.uk/maps?hl=en&q=yardley& um=1&ie=UTF-8&sa=N&tab=wl