1:9 probably is your best bet if you'll drop to 55gr or less sometimes. If you expect you might go with >69gr then think 1:7. Either twist *should* do well @ 62gr and I believe Del-Ton is 1:9.
I agree with Russ that a flat top is the way to go. Just put a good carry handle on now and you're set for irons. If things change down the road you can easily put on an optic. Heck you can even still use your carry handle if you hacksaw it down to look like the LMT rear sight. That gives you 4" of rail for a red dot to cowitness with your irons! I'm an iron sight guy too but now have a cut carry handle and RDS - best of both worlds.