Buying used disc mowers is a chancy thing. BTDT.
If possible, you should hear it run first. You should check for oli leaks in the cutterbar. Take the filler plug out of the gearbox, shine a light in, and look for broken gears. Don't but if any are broken.
Buying new: Buy whatever make a nearby, reliable dealer has.
The 3010 should have enough weight to handle up to a 9 foot mower. The 3010 has about 55 hp, dosen't it? That should be enough.
A 7 ft 10 inch mower is cheaper than a 9 ft and is enough for small acreage. The disc mower can be operated at high speed, as fast as you can comfortably sit on the tractor, unless the hay is very heavy. Also it will cut hay that is still wet with dew.
Reread your post, saw the 30 acre figure, so I don't think the 9 ft would be worth the extra expense.
Two types of disc mowers, the shaft drive which has a shaft running the length of the cutterbar driving individual cutterheads which have sealed bearing in them. Reliable authority says this type uses less horsepower to pull. In case you hit an obstruction and tear up one of the cutterheads, it can be repaired individully. I know of 2 makes of this type, Vermeer(whichI have and like) and Agco which sells them under Hesston, New Idea, and Massey Fergueson name plates.
The other type is a gear bed mower which has the cutterheads driven by a series of gears which run in an oil bath. Supposedly each gear acts as a small hydraulic pump which requires more hp to pull. Two main repair problems with this type: In case the mower hits an obstruction and a tooth is broken off a gear, the broken tooth can travel up and down the cutterbar and break off more teeth. Also, if the cutterbar has too much oil in it pressure will build up and blow seals and in extreme cases damage the gears. If careful attention is given to maintenance and the oil in the gearbox and cutterbar is changed each season, They will give many years of good service. Kuhn, Vicon, and Krone are good brands.
The New Holland has some of the features of each type. It is shaft driven and each cutterhead has its own oil bath.
Hope this helps.