I can't say what you should do, but I'll say what I did.
I've got the 21/4, 40/1.4, 90/3.5, and recently added a Jupiter 50/2 because it was cheap.
I've always got my eye on either a 90/2 cron, 75/1.8 CV, or 75/1.4 summilux when I win the lottery.
Maybe one day I'll add a 28mm. But 35mm is too close to my current 40 so not going to bother.
I'd also love a 50/1.5 M-mount Nokton (apparently the LTMs aren't so good), but can't afford/justify it.
If I were you, unless you really really like the 35/2.5 for size (I'm presuming it's smaller than the Ultron), then ditch that and keep the other three.
As nice and as cheap as the CV lenses are, they don't actually come up for auction on the 'bay that often, maybe one of each every week or two (trust me, I'm constantly on the lookout for cheap ones). So if you ditch one and then decide you want it back, you may have to wait a while for a cheap one or pay a higher store/BIN/keh price.