What is air speed difference of a 520 versus a 550 in a Bonanza A36?

Just a WAG:

At seal level, likely nothing.

At 10K, 3-5 knots.

There are wildly varying opinions.

Robert,

Normal LOP cruise speed increases of 7-8 knots in most A-36's on about 1/2 gallon more fuel per hour is the norm.

Your block speed will be even higher as your climb time to fuel efficient altitudes is reduced... and the ability to climb quicker to higher altitudes to take advantage of tail winds is improved.
Maybe a 10 knots stop to stop increase in "block speeds".

Don't know about "opinions"... but I've attached the exel spreadsheet data gleaned from the Garmin trip of every BT responder when I debated going from the 520 to 550 in my own A36.... and can back up that improvement in my own airplane ....now with pictures of my own before and after "trip page" statistics.

Leldon