122 Atk, 100 Def, 160 Spa, 120 SpD and same 110 Spe is what I'm getting for Latios. The Speed is quite disappointing tbh, though the increased Atk could make it a better mixed attacker.
Along with this data My associates and I over at my local server on showdown used a fakemon I implemented into the showdown local custom client to calculate mega latias stats:
using
we have gathered the following data:
haunter's guess is about right for latios
so far 80/93-94/122/140/150/110 are the stats we've gathered for mega latias with timid 4/252/252 timid mega latias
My quick analysis: I know many people say how useless it is considering soul dew exists but we have to remember 2 things
1) Soul Dew isn't released and won't be for a while in XY as far as I can tell and 2) Soul dew is quick banned in OU in most gens
Considering these 2 facts I can see the megas somewhat working, the megas' lack of speed tier increase is a bit disappointing but we have to rmemeber the lati twins already are prime speedy threats in OU, and their speed tier mainly doesn't need work done on it, I'm glad they used it on actual stats that needed it like bulk. Speaking of bulk, I think that was the biggest change, we have to remember that this bulk gives the latis incredible pivoting abilities with mega latias definatly having the upper hand in pivoting still. However like shiruba said, this also gives gives amazing tanking abilities letting them stay in on harmful attacks such as knock off (which stays at 65 BP due to mega stone!)
Speaking of knock off, comparing it to soul dew, I think aside from the physical attack and bulk this is the hugest difference- on mega latis they can't be knocked off and knock off caps at 65 BP as opposed to soul dew which gets knocked off and hits at a big 98 BP (round up)