If you want to get better at climbing then here's the 2 secrets - 1.do more climbing, 2.learn to deal with sustained pain, it's really that simple. 400 miles is a good little start, you'll get better as you rack up the thousands of climbing miles.

Forget your speed for now, you're better off getting a heart rate monitor and use it to work out your lactic threshold. To really get better at climbing you hammer uphill at (or very slightly below) your lactic threshold - it hurts but if you can deal with the pain you can hold that pace for quite a while.

I'm a bit of a clydesdale at 220lb so I have to work hard at being a better climber. I've worked out a nice hilly route to/from work and a couple of days a week I throw a 10lb weight in my trunk bag and do the entire route standing up out of the saddle at my lactic threshold. It's a real killer workout but in 12 months I've put on a slab of muscle on each leg while dropping 3 inches off my waist (almost no change to my weight), it's increased my average speed uphill by over 30%. As an additional benefit you'll be able to hold a higher cruise speed on the flats as well, a few thousand miles of hard climbing and 20 miles an hour on the flats will feel too slow.