Hello, I 've been also modifying my home oven, but it's gas oven, not electric.
The problem was, it was reaching only 230C(460F) degrees after 60 minutes of preheating.
So I've bought a cheap pizza stone (no other in our country), which helped a little, not very much.
Then I've tried a trick, that aluminium foil is reflecting warmth. I've put foils firstly only from sides, but then from all side. At the top of the oven, I've put metal sheet, with foil on its bottom. It also shrunk space the oven have, for pizza it's not needed extra space. (http://img708.imageshack.us/img708/5347/img0058lp.th.jpg)(http://img823.imageshack.us/img823/3157/img0001clo.th.jpg)
It helped incredibly. With last option, when I've covered even glass window with foil, I was able to reach 310C(620F) in 60 minutes. The oven was preheating very quick, it got to 250C(500F) in 20 minutes! See the differance, from original option, when it got to max temperature 230C(460F) in 60 minutes.
I have question although, can I go even higher, for example to 330C(660F) without a risk?