To run better, seriously, start by losing some weight. I've ran 35-50 mile a week for some time, also eating like a pig, and I just kept running worse and worse and gaining weight, in the end was unable to break 6:20 i the mile and 8:30 pace was the hard pace.. I took a two month break (5-15 mi a week just because it's hard to stop so suddenly), started counting calories and lost some serious weight. After that, I'm flying again :).
It's just not fun to jog at 9 minute/mile pace.
As for shoes, wouldn't worry about them. Best runners I've met (sub 4:30 mile) use Nike and Asics, and I haven't noticed correlation between shoe size and how good a person runs. A much bigger correlation usually appears to be between person's gut and how easy he or she runs :)
To each his own; I jog a 9-ish mile pace (4-ish miles) often. I find it enjoyable, and it provides good exercise, yet it's not daunting enough to make me drop the good habit.
It depends on distance. 1 mile, 6:30 min/mi, half marathon 7:40 min/mi.
There's quite a good formula that Pete Riegel came up with to predict your speed over a certain distance: T2 = T1 x (D2/D1)^1.06. There's a caculator on this page: http://www.runnersworld.co.uk/news/article.asp?UAN=1681. It's been pretty accurate for me, YMMV.
It's just not fun to jog at 9 minute/mile pace.
As for shoes, wouldn't worry about them. Best runners I've met (sub 4:30 mile) use Nike and Asics, and I haven't noticed correlation between shoe size and how good a person runs. A much bigger correlation usually appears to be between person's gut and how easy he or she runs :)