You may be right about Gilbert, but I remember seeing him chase a play 25 yards downfield to make the tackle. I think he's fairly fast for a DT. Has to be someone on the OL.
I'll say either Leander Jordan or Louis Williams. I think I remember seeing both of them listed as 5.+/40 guys. Gilbert was once clocked at 4.7 early in his career...doubt he could get that now.
When Weinke was clocked in the 4.8 range people were shocked. Let's assume he's there at a worst case situation.
I think Derrick Fletcher has the slowest recorded time of anyone with the organization right now, I'm not certain that anyone ever bothered to release a time on TJ Washington. Leander was listed at sub 5.3, as was James. I can't imagine Steussie's all that fast, and a post-injury Donnalley might lose if given a good head start.