D2D,
I train in Nike Lunar Elite 2 shoes, and while the flatness can feel slightly alien, I'd advise sticking to a set formula for a while and just concentrating on the running as opposed to chopping and changing.
I've now got a pair of Brooks Green Silence for upto 10k races, but wouldn't train in them.
You've got the promise and dedication for some decent times, I could easily envisage a sub 1.35 if you pushed yourself, but consistency is very much the watch word.
Good luck.
N.B - Can't say I'd advocate the attacks on D2D here, she's a pain in the arse sometimes, but this I feel is a rather valid thread - Don't click on her threads if you don't want to read what she writes.
She's hardly clogging up the site - Some threads have many thousands of posts and sit up at the top of the board all the time.