Finally gathered up my courage last night and inserted the V27.1 CD that I had burned. No problems at all - took about six minutes. I haven't had a chance to check out any differences between V19 and V22 on the MkIII, but it's nice to know that it's as up-to-date as it's gonna' be without upgrading to a MkIV.
Also got the 2006.2 CDs in from NavTec($50 off deal). Much improved coverage where we live SW of Atlanta. Even has all the streets in my little(60 homes) subdivision - nice surprise.
Patrick