I ran a solas concord 12/15 on my 650 boat and it worked well.
I had a pipe, and lots of compression too though.
totally stock you might need something different, in this aspect the older stle impellers work well also.
the old super camber ( SC ) solas impellers work well, and I have heard that the old SKAT 10/18 and 9/17 worked well also.
the 650 simply doesnt have enough power to pull much impeller in such a large pump I dont think.