As long as the hot end is hot enough, it really doesn't matter how cool the cool end is. The animal will choose the temps it wants and needs. With such a large enclosure, and the number and power of your bulbs you should have a really good gradient. By keeping the entire enclosure so hot you run the risk of over-heating, especially if air flow is low.
Of corse, you want your uro to use the entire enclosure, so you may want to heat the cool end, but I think 75F on the cool end is plenty warm.
Observe your animal and see what it prefers and adjust.