I think that the Oly 2.0 lenses are similar weight as the Nikon 2.8 lenses (zooms) - not discussing 100 - 200g more or less of course.
I am pretty sure that Oly lenses are equally good (or even better) than their Nikon (or Canon or Sony/Zeiss) counterparts - even if I open a rathole here.
But where it really comes to play for Oly 43 is the tele range. The Nikon (or Canon) counterparts are for sure much bulkier and heavier. Especially if you go for the Oly 2.8/95-250. Think about that, it replaces a 2.8/200, 2.8/300, 2.8/400 AND 2.8/500 (which I think is not even available for either Nikon or Canon - but I might be wrong). What comes closest is the 4/200-400 from Nikon but this is very limited compared to the Oly lens.
And I think also the "cheaper" standard zoom is not bad WRT IQ and DOF, but pretty cheap for such a great lens.
So I think it depends on where you want to go. If wildlife and extreme telephoto is your preferred area of usage then the E5 concept would win in my eyes. If it is more into available light and highest speed primes (1.4) then it is for sure Canon or Nikon. If it comes to highest speed AF and AF flexibility then it is also Nikon or Canon.
If it is highest resolution - so if you want to use your DSLR also for landscape - then I think it is better to wait for the next Nikon D4X or Canon 1DsMK4 etc, because those will be in the range above 30MP. And then you would not need a separate MFDB system with either 39 or 40MP - I know there are still differences in micro contrast and dynamic range, but they become pretty small actually.
But if you want a great overall DSLR system with excellent and high speed lenses, then the E5 and some of these Zuiko's are the way to go.
For me it gets quite clear the longer I think about this, that I might actually switch to the E5 and some high speed zooms. Plus add maybe the 1.4/53 Sigma with 43 mount in order to have a high speed prime.