My 4610 handles it good with the FEL on. I definitely know it's there, and it certainly is heavy, but it works well.
The best way I've found for it to work when doing heavy thick brush, is to put my top link in float (or use a chain for instance) and have all the weight of the mower on the two lower links of the 3 Pt hitch and also the tail wheel of the mower.
Without the FEL on, and the mower raised off the ground, I will lift the front wheels off the ground until the tail wheel hits the ground. I only did that once and now never remove it.
As a side note, the advantage to having a hudraulic top link with a heavy duty mower like this, is that you can raise the rear end of the mower a few feet off the ground, and back slowly into a tree to shred it. I do this all the time for trees that are too large (strong) to lush over by backing into them (they just stop the tractor if the back of the mower hits them at ground level while backing up).
I've cut some large trees this way.