Can it feed on the side normally or should it go on top?
Oh the frame is plenty strong to hold that spool if you mount it on top – and doing so would avoid the drag from hauling the filament through the tube from the side. But, I wonder if that much mass up on top so high might start “dancing” about a bit, particularly if the back-and-forth movement of the head at some point in time hit resonance… the result would probably be a less-than-ideal print quality issue.
On the side, the issue would be the ability to rotate that heavy spool whilst pulling the filament through the tube – should work, I’d expect. Would work better if you had a spool holder with bearings instead of the arm on the Taz that Lulzbot provides. But probably would be better overall than mounting that much spool on top.
Ideally, one would have the spool overhead mounted on something other than the printer itself. I have an ordinary dowel (a length of old wooden closet rod, polyurethaned, and sanded smooth) mounted to the wall above the printer. Heavy spools sit on that, and feed directly down into the printer. Works so well I’ve only had to use the Lulzbot-provided arm for my spool of nylon filament, where the center hole is too small for the closet rod.
If the large spool starts to turn, some times it does not want to stop. If you saw the spools in the AO printer farm they had sleeves on the arm to provide additional friction. So a bearing holder might unroll more than you would like.
I have used 3KG rolls on my Taz 6 several times with the sleeve I have.