Honestly, I think you can't go wrong with either then (6'1" is probably just fine!). I have both the duomid with solo inner and the solplex...which I purchased as a thru hiking solo tent (the duomid i use with my 80# dog).
The solplex and duplex have HUGE bathtub floors. I can't even see how rain would get in that tent even if you tried. A friend had the duplex on a trip with us and we had a HUGE downpour, with blowing rain, lots of scary thunder, etc. He was dry as a bone in there. So I think it would be just fine - but it is a single wall tent, so the condensation is an issue.
I guess it comes down to the flexibility of the duomid + inner (which has variety - with inner, without, duo inner, solo, double wall! if you want it) vs the solplex/duplex which is just the single configuration.
I really, really love the vestibule of the duomid/inner set up - but I found I sometimes have to search a little more than I'd like for a site because the footprint is a bit bigger than i'm used to. I also really, really love how small the solplex is, and that its only 14 oz with EVERYTHING included. That's pretty darned sweet, I must say.....