I have a 5’ <font color=green>JD</font color=green> Rotary Cutter for my 2910. When the weeds are high (over 2’) and heavy I have use low range to cut 3 acres of field. Engine will start to lug down at times and I have to let off HST pedal until rpm’s pickup again.
I run in mid range when weeds are 1’ or less. Engine will not lug down even at full HST speed.
The height and type of field you are cutting will determine what speed and size of rotary cutter you can handle with a 2910.
In the 2910 manual <font color=orange>KUBOTA</font color=orange> recommends a 48” rotary cutter weighing 500 lbs. My 513's weight is 508 lbs.
There are many discussion on TBN about Rotary Cutter size. Try using the search feature at the top of page. Plan on spending a lot of time reading. This brings up a lot of threads. /w3tcompact/icons/eyes.gif
My opinion is that the 5’ is proper size for a 27-2910 tractor.
I've been using a 5' Landpride rotary mower for about a year now and have had very similar results to what RonH has had
with his, but mine is a B2400 with 1100 hrs on it. I agree that the 2910 should easily take a 5'. Good Luck !
Rob