Used stock RB600 or new mod'd 250?

Sorry if this has been discussed before -- I didn't see anything though, besides debating which mods.

These seem to be roughly the same price ($450), which is the better route? I'd probably land up keeping it for many years, so it's not really a stepping stone to the next arm.

It would be mounted on a Systemdek IIX and mated to a Grado Platinum cart.

BTW -- the 250 would be an Incognito rewired OEM, with either Expressimo or OL weight.
I'd use the modded 250. According to the OL website, a modded 250 exceeds the performance of all other unmodded Rega arms.
I agree with Twl. My old OL Silver beat the pants off my RB600, so I'd be willing to bet that a plain vanilla modded 250 from OL is still better than the 600.