We have the older 'Advanced Rules Set' option which includes the high speed tool options
Apparently, there is no way to designate a set of nets into a class and then have them all DRC checked to be within a certain length overall or to each other.
Is this correct?
Here is the help file note on the 'matching option' of the high speed tools, note that it seems to be just for autorouting and there is no way to DRC check it.
Some routers can automatically route traces with matched lengths. For
Restriction: PADS Layout does not check length-matching rules.
PADS Layout does not natively check Matched Length violations, however, you can use Tools > Verify Design > Latium Design Verification with 'Trace Length' enabled in the Setup dialog. This will run the checking routine behind the scenes in PADS Router on Matched Length violations and return the results to the Verify Design window in PADS Layout.