I think if you want to do a speedy groudon you should go all the way. Maybe replace it's iron head for rock polish so it can blitz through things that used to outspeed. In any case the previous quote about it not needing iron head is true. It can neutral damage xerneas to death and only is threatened by it having hidden power after it gets geomancy off. Plus it can counter other groudons if it can get it's polish off before they come in with that guarantee'd outspeed.
It's also correct that you need some speed control. Especially since you're running max speed on everything bar ferrothorn. Get some icy wind or electro web or something in there. I'd say that other thundurus would be better for you as it could secondary t. wave with ferrothorn. It could also taunt incoming trick rooms, which is something you should really keep in mind cause there's some bros out there with mad trick room game. If someone is able to get a bulky character in and trick room on you, especially after xerneas' geomancy speed comes into play, you could lose all your momentum and burn out.
It's also correct that you need some speed control. Especially since you're running max speed on everything bar ferrothorn. Get some icy wind or electro web or something in there. I'd say that other thundurus would be better for you as it could secondary t. wave with ferrothorn. It could also taunt incoming trick rooms, which is something you should really keep in mind cause there's some bros out there with mad trick room game. If someone is able to get a bulky character in and trick room on you, especially after xerneas' geomancy speed comes into play, you could lose all your momentum and burn out.
Ermergerd sergnercher