Post got the big one: Total Store Ordering (TSO).
The rest are all techniques in reasonably common use, but unless you have hardware support for x86's strong memory ordering, you cannot get very good x86-on-ARM performance, because it's by no means clear when strong memory ordering matters, and when it doesn't, inspecting existing code - so you have to liberally sprinkle memory barriers around, which really kill performance.
The huge and fast L1I/L1D cache doesn't hurt things either... emulation tends cache-intensive.
replies(6):