The trend in direct seeding has taken us back to slower seeding speeds which in turn has led to much wider drills and ever larger tanks and more of them. Bottom line is much more weight. Not such a big deal on flat, firm ground , but in any adversity (hills, mud,etc.) is where the need for a lot more weight and power comes into play. My experience over a few decades is that the tractor should weigh a minimum of 1/3 of the gross weight of the whole rig. That is not excessive and more is still better. I upsized my seeder and both tanks a few years ago on a tractor that had been working well for many years and just killed the performance. Tractor was now 1/4 of gross weight. Way too much iron dragging behind. Time to upgrade tractor, up to about 44% of gross and the tractor was amazing in mud and hills. That 44% included 8600 lbs of tbt hitch weight which is a big factor in total pulling power. Horse power is important, but kind of secondary to the ability to get the power to the ground. As far as turning up the pump on the old tractor and hooking twice as much weight behind it, not a good long term solution. You will find a comfortable gain with the 505 hp tractor that is designed to handle the additional power, torque, and weight without overstressing everything. Just make sure it has enough weight built in to hold down 505 hp. Like 50-60,000 lbs working weight. Good luck!In between cleaning up rockpiles, helping the neighbours finish combining, and other field work, I'm looking out for a tractor for next spring.
I have a 2002 Buhler 2360 (N14) that tows a 4000us gal TBT liquid cart, a 70' Salford 525, followed by a Bourgault 5350 air cart. In perfect conditions I can get by, however getting rolling is hard on the clutch. When conditions arent perfect, though, I seem to be doing about 120% of what a 360 hp tractor is capable. That's a guess but it can't be far off.
I'm looking at a 2011 T9.560 with 700 hours. Would 505hp be enough of an upgrade?