IXB vs. IXC

[danoh]

Hello, I've belonged to SubSim for a couple years, but have recently returned to playing SHIII - this time with the superb GWX mod.

I chose the Wilhelmshaven fleet and ran a VIIB for the first few patrols. After being transfered to Lorient I then took the IXB. On the very next mission the IXC became available. But after comparing the stats it appears except for improved range and an extra torpedo (?) the IXB has most the advantages, such as a slightly faster dive time. Is there any advantage of the IXC I am missing?

I understand based on what I've read on these boards and know from history that things will get increasingly dangerous as the war progresses (currently it is January, 1941). My plan is to run a Type IX boat through the summer of 1942 so I can have my Paukenschlag tanker party off the U.S. coast. After then I imagine switching back to some kind of advanced VIIC model that can manuever better.

Does anyone know about what time I can expect the VIIC/42 to show up as an option for the Lorient fleet? Is it correct this model has a lot of upgrade options and gives the best chance of survival when things get really bad after 1942?

Thanks for any tips you can share.