Hopefully the altidude wont effect you too badly and any mild effects will soon be forgotten when you are gazing down at the East African plains and looking across the crater rim - definately worth all the hard work.
As for the scree run on the way down - wow!! Several minutes to get down what took you hours the night before!!
The other routes are also meant to be more scenic. I had also meant to say that on my trip all of the long distance runners made it to the top - so it is definitely worth putting in those long runs. As a runner you will be no stranger to drinking loads (not beer!!) - make sure you drink even more on Kili as you dehydrate quicker at altitude and it kind of helps thin the blood. Personally I would avoid taking Diamox. Have a good trip.
Hi - I did Kili with Explore and it was pretty well organised although we did not have an English guide. We did the standard Coke Cola tourist route but we added an extra days acclimatisation to Zebra Rocks. Don't think that the tourist route is necessarily the easiest route. Usually because less time is spent on it it has a higher failure rate therefore if you have the annual leave try one of the other routes.
I would also recommend KE (Office in Keswick) - I did Mera Peak with them and it was a very well organised trip with English guides.