Stay with the Trek 820. Build up the best you can and use it as a learning tool.
Given you rid a 58cm, I would go with a 622 (700c) sometime in the future.
I have two commuting bikes (9 miles/14˝km each way); one a PDG70 with 559 rims, and the other a Trek 720 with 622 rims. The Trek is heavier, but ~5% faster on my mostly flat (6 under passes) route, and rolls nicer. The gearing in terms of GI (compensates for the tire size difference) is about the same. The Trek has 28-622/35-622 tires, the PDG 32-559/40-559 tires.
I also suggest that you be on the look out for: Trek 930/950/970/990/750/790/520 in your size, and avoid suspension versions.