Depends on how big of an improvement the new standard driver is over the old one. A Shiva sonotube with a 250W amp would have easily bested the old 20-39PC. But with the new amp and the new driver, I'd imagine it would be a much closer comparison now. With out T/S specs on the new driver, or objective comparison data, I won't hazard a guess as to which one would have the slight edge. But I will say depending on the improvement in the new standard driver that edge will be small which ever direction it goes. Hell they might even be equivalent.
A Shiva sonotube you propose would be equivalent to the Dharman if it had a net internal volume of 109L and was tuned to 22hz using dual 3" flared ports. Take from that what you will.
To add to Colin's list, if you have the tools the Shiva sonosub can be a chunk cheaper, like almost half as much.
There was one comparison done and posted at HTT a while back...you might be able to find it with a search. The HT enthusiast was comparing the old 20-39pc to the dharman. It was a wash (although he didn't send the 20-39pc back for a refund) more or less.
Unless the diy sonotube was designed to outgun thedahrman I think a 39PCi would compare very well.