Determine highest cell value in column

I need to be able to highlight the largest cell value in a column. It's not as simple as it sounds- the column in question contains strings, not numbers. I have a classification system for DVDs that I burn, and I keep track of them by giving them each a unique ID. For example, Disc 1 might be D-0001, Disc 2 would be D-0002, etc, except that I use hex numbers (instead of 10,000 (10^4) unique disc IDs allowed with 4 digits, I can have 65,536 (16^4)). For example, Disc 9 would be D-0009, and Disc 10 would be D-000A, and so on. So it is a string containing a padded hex number. You might ask, why don't you just look at the last ID in the column? Well, to further complicate things, I also group the discs in to certain groups, with a unique group ID, such as G-001 (also using hex numbers). Groups can have 1 or more discs in them, and I sometimes have to go back to an older group to add more discs. Obviously, the unique disc IDs have to keep incrementing, so I end up with a jumbled column of disc IDs, and an "alphabetized" column of group IDs. I have to search the disc ID column every time manually for the largest number so I don't repeat the ID. I'd rather not re-sort by disc ID because I have gaps in between chunks of unique group IDs, and I would not be able to get this back with another re-sort.

How might I go about converting this disc ID to a number so that I can use conditional formatting to highlight the "top value" in the disc ID column?

Thanks! That works perfectly, and I can hide the helper column when I need to.