I have found that the #11 plate works very well for towing in my 5 sp truck. As the egt issue goes, as long as you don't get radical and slide the plate foward, you should be fine on egts. If you find that the egts are getting up there, just take a minute and slide the plate back 20 thousand.
As for the 16cm housing, it will lower egts some, but at the cost of low-end response. You will need to increase fueling at low-end to make up for the lack of response, which will increase smoke.
I would check your cat first, most likely that is where your restriction is on the exhaust.