I have crossed St Clair on a 96 XP on a perfect day in early September and once you get out into the blue (When the water actually starts to look blue) you can count on 1 to 3ft seas. Like I said thats on a perfect day with little to no wind and lots on lake traffic. I have also rode from Sandusky bay out in to Lake Erie and down the coast. The key to riding the X4 hull in any big lake or ocean condition is riding slow (10 - 15mph) and parallel to the waves, riding directly into the swells will make life very difficult very quickly. Obviously you should do your homework on conditions that day before heading out because you do not want to be caught in anything over 3ft seas riding that hull. Prepare for a work out, Take your cell phones and tell people where your going before you leave.
If you take the route that I think KK4 is talking about your round trip would be approx.41 miles If Im taking you thru the right channel. Make Google Earth your friend.