I haven't had problems with a Squall or a Squall2. I have used both in moderately strong windows (say to to 45mph), in driving rain, without significant problems.
In regards to keeping the tarptent taut… when you pitch it in good weather can you get it taut? I have notice some pictures on the web were I could see ripples in the material. A properly pitched tarptent is very sleak. If you don't have a problem getting it taut under good conditions then there are three things I do. First, I modified the front guylines to be adjustable, so when the silnylon stretches I can easily shorter the lines to compensate without restaking. Second, I place the front pole at an angle initially so that I can raise the front slightly by moving the pole. Third, I have found that the back hoop pole can move around a bit making the tent less taut. I will often place a large stone in front of the rear poles to keep them from shifting.
Windblown rain? Not had a problem. I have pitched the tarptent a bit lower to the ground that normal. Splashing? I haven't had a problem. If I expect rain I make sure to select a site where I can sent up in the midst of durable vegetation such as a field of grass. Maybe if I was stuck somewhere with nothing but hardpack I would have had problems with splashing, but so far I haven't had any splashing problems.
As far as rubbing against condensation on the sidewalls… I found two issues. First, if we were on a slope I would tend to slide. I applied sil-sealer to the bottom of my pad and this no longer happens. The second issue can be moving around without keeping in mind where the walls of the shelter are. Part of this is practice. Using an even smaller shelter can really train you to be careful :-). That said, so people seem to adjust, and some people don't seem to develop the situational awareness. For example, my daughter can't seem to stop kicking her legs up and she isn't so careful in her movements. She regularly brush against the sides of the squall and squall2. I solved this problem by switching to a Double Rainbow on the trips that she is sharing a shelter with me.