IMO 88.2 would be the sensible frequency yes.
And yes synths
should render better at those higher frequencies due to reasons I can't be bothered to type. basically the calculations are done better.
but - remember that many VST programmers can forget to make processes sampling rate independent. That means when the sampling rate goes up the sound goes crazy!
So that means anything from LFO speeds, to filter calculations, to in extreme cases oscillators (!) This sometimes happens with the 'big name' vst instruments as well as the freebie ones. These sampling rate dependency errors are more common than you might think.
anyway - if you have a load of vsti running at a higher sample rate to file - check the 88khz mix closely to make sure there isn't a crazy high speed LFO, or an odd sounding distortion, or a slightly more open filter buried in the resulting mix somewhere . You don't want to get the master done and notice it then!
essentially you would gain from the VSTi running at a higher rate - but you also have to make sure the output is what you actually want. Many sounds become worse when they are calculated 'better'
Alongside that VSTi calculation improvement though, you have the downside of any samples being affected adversely.
Until I can work at 88 all the time and my samples are there too, I am sticking to a 24bit 44.1 workflow.