If it scores a count at
Overture WITH the extension included you can be fairly confident it gets typo traffic..
For example the typo of miniclip.com:
minicilp.com registers 296 which is excellent.
There is no way to ascertain the actual traffic it will get but using experience and judgement as to the quailty of the original target domain you can gauge an approximation.
I have names that register uniques at double the OVT+Extn count
but more that register as low as a 10th.
I have never gotten round to finding out an average (though youre question gets asked a lot) but I would guestimate it, in my case, to be 1 click per every 3 counts on OVT+Extn.
This will be different for everyone, of course.
Hope that helps and makes sense !