Muhle STF for the win. Closest to a silvertip I’ve come across.
+1 the STF is the easy button choice. It splays more than the super stiff Tuxedo and has much softer tips.
But the Razorock Bruce and Big Bruce are fantastic splayers and are very inexpensive. They have less backbone than the STF and splay 2-3x their size willingly.
Two days ago I used an RV 25mm STF as a preshave brush and a 28mm Zenith Badger as a shaving soap brush. Seriously, you could be forgiven for not being able to tell the difference if blindfolded. The tips are the giveaway, the STF's are unnaturally soft compared to the badger, but the backbone, splay and relative feel were very similar.
The STF splays but not A LOT. The RR brushes splay significantly more but have far less backbone. I ended up giving the RR brushes away and keeping the STF but like @Phoenixkh I prefer a firmer brush generally.