Some random numbers. I went generous on the items, but not for any particular reason. Every setup is assumed to have mana/lvl utility mastery, mana/lvl seals, 7 flat mana glyphs, and 3 flat mana quints. Bonus damages are mainly what I'm trying to showcase here, but I've also parenthetically taken note of Overload's extra base damage.
Level 6, Catalyst, Boots, Tear charged to +100
New: 87 (+20 base), 60.3, 13
Old: 106, 70
Level 11, (Boots, Odyn's, Shroud, Tear w/ +300 bonus mana)
New: 170 (+20), 117, 26
Old: 207, 138
Level 16, (Odyn's, FH, Tear charged to +400)
New: 189 (+20), 131, 29
Old: 235, 157
For lulz, level 18 damage with a full build (Odyn's, FH, WotA, Void Staff, and a fully charged Archangel's, which obviously would never happen in Dom, but still):
New: 383 (+20 base), 366, 150
Old: 377 bonus damage, 397, 109.94
And some slightly more realistic numbers, with a partway charged Tear (charged to +600) instead of a fully charged AA's:
Old: 3745 mana, 310, 264, 52.5
New: 3520 mana, 288 (+20 base), 248, 87
I think the main difference we'll see is that Ryze will try to build WotA, Void Staff or AA's a lot earlier than he normally would. RoA isn't really a great Ryze item, but I'm sure we'll see even more Ryzes building it than usual "because AP is good now."
imo the ratio on Spell Flux and the flat +20 damage to Overload will make tanky Ryze's build slightly stronger or about the same at 1-6, then he'll fall off some from 9-16 (compared to his old build), then very quickly spike upwards.
I don't see much motivation to build a bunch of AP and go glass, like Morello has been talking about, especially with Ryze's low ranges and the fact that bruisers with gap closers are still hugely prolific. Tanky Ryze still gets more than enough bonus damage from building mana.
. Imo, the range nerf on Q will mostly hurt his team fighting, but the improved bounce logic on E could make up for that. I could also see him having more trouble 1v1ing champions with longish range targeted abilities. Irelia, for example, will be able to bladesurge onto him right as he's able to attack her, whereas before he could Q and run a little bit.