That's unusual. I've been running 4.6 for ~2 days now with no issues (clocked at 250). You can see from my hash results that there's been no significant performance difference:
https://www.miningrigrentals.com/rigs/491That small dip on the 8th was me upgrading.
It is unusual, 4.6 has been out for justa acouple of days for starters, and I was running ar 262.75???
But I'd say there certainly is an improvement in the hash-rate, if only (as attested above) attributable to a reduction and hash-variance.