Nothing wrong with staying with your favourite shoe Naomi. I've had pair after pair of Asics 2170s for 3 years and I'm sticking with 'em. Really surprised that your new pair of Omnis was so different though. That must be really disconcerting and I'm not surprised you're wondering where to go from here. Have you tried returning them and getting another Omni 8? - you could have had a dodgy pair that fell of the production line? it happens.
However long-term, the gait analysis IS the way to go. Though combine it with your own instincts. My local running store offers it but like yours only stocks a few brands (luckliy Asics is one of them). If I were you I would give myself a massive day out to your nearest big running store. (I could spend all day in mine). Someone will watch you on the treadmill and show you the video so you can see what's happening. You will then try on dozens of possibly suitable pairs, have a little trot in each and choose your favourite.
You might be surprised too - I (and my gait analysis guy) was shocked to see that I do NOT overpronate despite having the flattest feet in the human world. I could go for neutral shoes but the stability of the Asics 2170s seems to suit me and they're not doing me any harm. Last time I went for slightly different Asics Gel DS, as they are a lighter version of the 2170s for speed/races. These give slightly less support and my calves have had to strengthen a bit but all good now. I alternate between running in the DSs and the 2170s and just update them when they're knackered (when I get a random surprise new niggle somewhere I know it's new trainers time). I am tempted by some of the pretty Adidas ones and Nikes look cool but if it ain't broke... I tried out some Brooks just out of interest as a friend loves them but after 2 miles I cried all the way home... When you know, you just know.
"Zitty head"!? ... an image I'd rather not have in my mind....
Tried a snowy run today tho gone slushy here, it was fine once I let go of my target pace and turned it into a fartlek run. Speed up on the clear bits recover on the icy bits. Extra aches tonight tho, it must change your gait, tenses you up I suppose. No falls thank the lord. 5 weeks til HM - trying not to lose touch with the training plan but refuse to go deadmill... but it is a great experience to be out there in the snow.
I'm curious too. My hunch says 'incompatible'. This diet utterly flies in the face of everything I've ever read/been advised: small regular meals, snacks to maintain energy levels and avoid blood sugar dips. Got some friends on the 5:2 diet raving like some loony cult members. But they don't run or exercise much at all in fact. I reckon it's hard to do 20+ miles a week on any restrictions. Having said that I feel great (light fast energetic) when I run early morning no breakfast. Only for 6 miles tho, more than that I crash: wobbly legs, nausea etc. I wonder tho if it can work, it does seem to have a basis in proper science and some real converts.