10" f/5 secondary mirror

Hello, somehow I got some wierd spots on my secondary mirror that don't want to come off, I even tried some acetone on them. Any way I was thinking of maybe replacing it with a secondary from protostar. My mirror is 63mm or about 2 7/16 inches. The closest size they have is 2.14 inches I believe. Would this mirror cause me to lose some of the light cone from the primary? I don't want to waste any light the 10" mirror grabs. Or do mass produced scopes have secondaries bigger than they need to be? I would just use the existing spider and mount, and cut the sides off the mount and RTV the secondary to it. Thanks

They have 2.6" in quartz, but I only have a 2.6" in a 15" DOB, so I would thing the 2.14" would be fine. Newt shows a 1.84" for the 10" f/5.6 and shows no problems with a 2.14" as well.
You might go to this page and check all the specs out yourself.
http://home.earthlink.net/~flyj/designie5.html
Floyd