Looking good! I wouldn't worry too much about the difference in wheel surface speeds. If you use enough force to switch between wheels you'll have almost no simultaneous contact.
A few suggestions from the top of my head:
- The traction wheels are used for pushing and staying in place. It may make sense to switch the wheels such that traction mode gives you the largest wheel base.
- That seems like more than enough ground clearance for your traction wheel when it's lifted. You could easily be comfortable with .25" of clearance when either wheel is lifted (game dependent). This will also give you faster switching between modes for the same diameter pneumatic cylinder.