According to the product documentation, 11.5x does not "upgrade" 11.0 scripts. As long as you don't implement anything in the script that is only available in 11.5x then you should be able to continue to run the scripts using 11.0.
(Opinions and information contained in this post are wholly my own and do not reflect the opinions of my employer.)
With you information I can use UFT to move the scripts and files to QC 10 knowing that if I get the old QTP machine working with QC I can work on the scripts from both machines. Hopefully I can get away from QTP soon.