Here in the arid west, I find that Gene Yale's preferred M27 and P22 seem a
bit uncomfortable, although they are surviving and working. I've had better
luck with Bud-9 and Mark, which you might consider as alternatives. I avoid
M-9 due to fireblight susceptibility. Ott-3 works good too after it's going,
but it's a real job to get it started as a rootstock -- mine weren't started
here.
My closest trees are 2.5-ft spacing, trained as oblique cordons on a
post-and-wire trellis. Requires a lot of pruning. Top wire is at 7 ft to
minimize ladder work. I like the trellis for avoiding wind damage to the
fruit, since 70 mph winds are routine here. Rows are at 12 ft apart.