Size doesn't always equal strength. I only dead a bit over 300 lbs for 5 reps and I'm 220 @ about 12% right now. There are a lot of neural adaptations to also consider if one does not deadlift that often. I'm sure if Colby did some training focusing more on strength, he'd probably see some rapid gains in his squat, dead, bench and row, but with HST that won't happen quite so much. Rapid strength gains aren't always that good though. I was doing 5x5 and gained quite a bit on my squat, a bit on my bench and row, but my joints are beat to crap...
Still, the disparity between size and strength is another reason I would advocate focusing on strength for a while between every few HST cycles. Some people don't take well to 5x5 and that's fine, there are other strength protocols that are just as valid. HST could easily be tweaked toward this fashion as well.
I'd highly recommend it for you sometime, Colby. You're a young guy still, so I'm sure you could add a ton of poundages to your major lifts in a short period. That would surely assist in your next HST cycle after that as well, since you could use larger increments and so on...